OK I've seen this kind of pingpong a lot. I wrote my psychology doctoral dissertation on children of divorce, and he obviously is one, and also a reallife divorced man himself. You probably have intact parental marriage, so you expect people you love to be trustworthy and not abandon you, where he expects the opposite.
The only human constant in his life (aside from fragmented parents) is his son. But his ex has more control over her child than he does, and he gets to look like the bad guy in that relationship more often than not. So proving he's a good father is one of the shame/guilt traps he's struggling with. And you have no power to counter that, unless you give him a child and give him more control over it than she does--bad Idea, obviously.
You know in your heart that he's never going to "work it out" with the mother of his child. He's had enough chances to prove that.
But here's a really special pattern of relationship that boy and girl children of divorce can sometimes enact. I owe this understanding to a now 40 yr old female student who experienced it with her lover when she was 25 and in my Psych of Relationships class at my former college. It's called serial monogamy with the same person, or better yet Serial Divorce and Paradise Lost and Regained.
Here's how it works for him: He might well have gotten dumped by his first love. OR he fled from her when things got "really bad" because she was arguing with him. Since that's what bothered him a lot before his parents' divorce (more or less, this is a generic game-plan), he "knew" once uncontrollable arguments came along that that relationship was "Doomed" and it was just going to get worse and more painful for a long time before ending. So he bailed out, because at least then HE was in charge of the ending, he wasn't getting abandoned and feeling helpless to prevent it.
My own quantitative divorce children research showed them far more likely to be the first to dump a relationship, sinceTHEY DON'T WANT TO BE HELPLESS IN LOVE EVER AGAIN.
Love and Power are a pair of opposites that is central to love relationships. Lovre & :Hate are not the opposites, because when you Hate you're just as attached and dependent on the other for your well-being as when you Love. But if you wield enough power in a love relationship, you'll be able to fool yourself into not realizing that you're just as dependent on your partner as she is on you. And Power Corrupts. Unbalanced Love&Power relationships are a living hell, as you've had ample opportunity to experience..
Children of divorce don't like being without a girlfriend, cuz they'd feel their intense loneliness and be reminded of all those other times when they couldn't get the love and security they needed as a child and adolescent. So they get a new girlfriend: Enter You.
But as soon as the going starts to get rough (or when there's a good-looking chance to get the lost mother of his child back under his control) he starts thinking Oh Sh*t, it's happening again! So he leaves HE DIVORCES YOU. In fact he's already done this so many times with so many girlfriends, casual and "serious." For he gets passionately involved VERY fast: he needs to test-drive this new buggy to find out if this one will be argument-proof and divorce-immune before he's wasted too much time and emotional commitment, tho he's not conscious of this power-maneuvering.
In fact, he's so practiced at divorcing that he's used to all the sweet sorrow, and it might even be somewhat satisfying to see his girlfriend(s) suffer a lot when he leaves (even tho it's a guilty pleasure), since he suffered like that when he was a kid and NOBODY HAD TIME TO CARE.
So he goes away, perhaps samples some greener grass in another pasture and finds out it turns rocky too. Then he comes back "You're the One I really want! You're the BEST!" And you know what? IF you take him back every time he comes to your door, even if you're a bit peeved about it, YOU ARE THE BEST. For you can go thru the pain of getting dumped and divorced over and over and STILL LOVE HIM enough to take him back. Here's the secret of this pattern:
Serial Divorce is a great pattern for an adult Divorce-Child to swerve in and out of closeness, and get a little closer each time, after his loyal missus takes it on the chin half a dozen times and lets him back in the door anyway. Serial Divorce is a way for him to edge closer to a full time commitment, even tho every time your relationship hits the rocks he's going to have to take defensive measure to stave off his old abandonment wound, like making sure he has a couple of backup babes in the dating sites to use as liferafts..--A divorce-kid will sniff the oncoming doom, the underwater iceberg, way before the nondivorce-kid partner begins to worry about that little knob of ice floating on the surface nearby. So he's still going to keep going away and coming back even if he doesn't actually run away from home every time.
Paradise lost and Regained? I won't go into this aspect much, but it's just an exaggeration and powerfully motivating pendulum swing that normally only goes a couple times in the breakup from a long term love. But for the divorce child, it becomes a way of life with plenty of drama. And as long as there is reason to believe that reuniting will restore the paradise of new love, then both partners can have faith that the relationship will be better than GOOD, really GREAT, as soon as all is forgiven and the Eternal Present is Paradise again.
This is enough info to choke a horse. But it's a great pattern. And conceivably an endless cycle that will go more seasons than Lost and 24. but for one thing. Even tho "Clouds won't hide the Sun" (Hawaiian Wedding Song, sung by Elvis Presley) in Paradise Regained, you can't forget that the Rainy Days may very well come back again, and you, the loyal Missus, are powerless to stop them. Who wants to give up on a Paradise that shines all the brighter because it gets rained out every so often.
And there's another down side to this Paradise-Manic-Depressive emotional rollercoaster: With all this intense emotion running the show for both people, you're not paying much attention to evaluating whether you're really Good for Each Other and have Compatible values, interests, families, careers and life goals or not. That's a rational consideration, and you need to explore it, FOR YOURSELF. Not with your Ramblin Man, because He doesn't usually know who he is as a love partner, and if he's building a career, it's at least partly as a shelter for his shell-shocked soul, so it's more self-serving, self-preserving than a genuine love contribution to the world around him.
I just gave you ONE clear strategy to help you make up your mind about what kind of a future you want: He's only able to do Love/Power, Courtship/Abandonment until he might some day discover that there are other ways to do his life. He's in his life for his self-preservation, with Love as a Tragic Inevitability. You need to do your own values clarification, especially about career, and spiritual and social life goals. Then you might be able to know that he is not right for you, even if he could reduce his pendulum swings between in love and out again.
I had that same kind of relationship for 3.5 years during my 30s. I never counted, but assume I got dumped 12 times, and it only finally stuck, when she induced a German backupguy to leave his wife I fly to America to climb into her spiderweb. Then I got a chance to see clearly that she could NEVER stand for me to be a very intelligent Professor (tho not so employed at that time) and a Psychotherapist. That whole real world career part of me was OFF LIMITS in her underwater mermaidworld.
Write back later if you have trouble shutting him out, because he WILL bang on your door a lot of times. And he will probably flaunt a few honeypots he's hypnotized, just to make you eat your heart out. You may have to shut off every "mutual friend" pipeline for gossip. I'll think about other issues. In fact right now I have a 42 yr old male client that's embroiled in 2 criminal cases, one against him for domestic battery (all false accusations by her) and one against her (for lying to a cop and accidentally/negligently destroying 10K worth of digital photo equipment that is the core of his career, and she also played a role in him being fired from his local professor job after 7 years--but he still says "She has my heart in her hands." (So I said, Yeah VOODOO Doll-Heart!) And I've assigned him to make a series of unconscious-art drawings starting with the heart/hands image, because the artistic creativity is one of the best ways to work your way out of a love trap like he's in. And you're in. So if you have an artistic capability (whether saleable or not) you may be able to use it to set yourself free too. Write me if you want. I've a website under construction, GreenEarthCollege.org where I'll serve people in more ways as well as relationship counseling.
He's not going to give you a definite answer, because he wants to keep his options open, that means your door, and his ex (or "ex ex") in case a new conquest doesn't work out. If my previous analysis is right then you're the BEST if you're the SAFEST, meaning that he can leave whenever the going gets rough & he smells a breakup coming (even tho you don't smell it), AND he can come back when he's quieted down and/or his latest newlove turns out not to be any safer or more gullible. My own passion pit for 3.5 years became convinced that she couldn't marry me, because SHE knew I "wasn't her type", so she tried to get more honest about letting go of me. But she still COULDN'T. In that case there was also a couple's astrological composite chart that showed clearly that the sexual/romantic chemistry was quite unusually strong, and neither of us had ever had that much magnetism before. But the relationship was still very limiting outside of the bedroom. The clarity of that chart convinced me that I ought to learn composite relationship chart casting and reading, so I did (later). Five years after shutting the door on that passion pit, I met my therapist wife, who is a well trained astrologer as well as a Jungian therapist. She didn't believe in testing relationships with a composite chart and didn't study relationships that way in astrology. But I did, and I found that the chemistry of her and my chart was "almost" as compelling in the bedroom, but more comfortable in the rest of life. She and I are mental equals and intellectual and artistic creators, and our therapy ethic, to focus on our psychospiritual growth for the entire lifetime as another dimension of living that makes life richer despite its share of troubles and tragedies. That psychospiritual part is a clear case for knowing where you want to go in your life and what your highest values are. But we were both over 30 and veterans of a lot of personal therapy, so we were people who had that serious, religious/yoga commitment. Other people might not recognize any more specific high values besides having a healthy family life and being devoted to their mate, and perhaps sharing a faith in God, or in Science, or Wealth, or Doing Good for others, etc. I have occasionally done coomposite charts on client couples, but they never take the results seriously, so it's just a parlor game, like a ouji board.
You said you know your rambler isn't right for you because of the way he treats you. That doesn't prove anything about whether your life purposes, values, etc are common or not. All it does is show you that living together would continue to be painful and impossible, unless you're OK with being that Cinderella that Prince Charming sees once or twice a year.
I repeat: HE'S NOT GOING TO GIVE YOU ANY DEFINITE ANSWER, because he wants no obligations to tie him down and HE DOESN'T WANT TO GIVE YOU UP EITHER. Your indecisiveness is not blameworthy. You are living in an ADDICTIVE & OBSESSIVE LOVE that's based in your own emotional & sexual biochemistry. You can get tired&disgusted with this love when your memories of his self-centered & hurtful betrayals always pop up like Surgeon General's Warnings before you take that next cigarette. You can reduce your love-dependent biochemistry by taking a Prozac family antidepressant. You may be able to flood out your passion-trap (where being reunited = Paradise) if you can devote your energy to a project, or career, or artform that puts you into paradise because it's so exciting and fulfilling to you. Or you can find a new lover and turn on your bliss to him and leave your rambler behind. Finding something you have love for because it fulfills you is the most independent and self-expanding way to reduce your dependency on a particular person. Instead of a "one and only" forever after marriage myth you'd embrace a love affair with the world around you. That true monogamy forever after is possible; I have it, tho it didn't start till I was over 40 and my wife was 33.