You're in a really tough spot. He has the power to choose his path forward and the RESPONSIBILITY that comes with it. When his exwife was engaged with the other man YOU had more power of choice and more Responsibility as a result. But it seems that you didn't exercise your power, because you allowed your partnership to go on and on without asserting yourself for a more binding commitment from him. In society since the 1970s the traditional assumptions about coupling, including that marriage is the only formal commitment that has a good chance of standing the tests of time, have been ignored by so many people that they have to relearn some by painful experience.
It's important now to assess what power of choice you do and do not have at present: 1. have you been living together for 7 years? If so, does your state recognize "common law marriage" and have laws that guarantee you some rights as a spouse? (You could probably get legal advice locally, look it up in your library, or ask about your state's laws on JustAnswer.)
2. Is your boyfriend a man who wants to marry you? Or has he consistently kept you at arm's length(marginalized) from his family life, so his kids wouldn't get upset and reject him in favor of their mother? Does he waffle or refuse to choose who he wants to be loyal to? Do you suspect that he might be enjoying his revenge against his exwife and also being the guy that both you and her want?
It is instinctually normal for humans to have the initial passion in their sexual relationship simmer down by the time that 3 years have passed, tho this passion can be extended if there are recurrent obstacles (like distance and intermittent contact) that prevent them from "settling down" to something like consistent cohabitation. Since you did not enter into marital commitment with him by the 3 year point, but have continued in close relationship for 4 more years without that, it is quite possible that you are as familiar to him--with both your attractive and disturbing aspects--as his exwife is. She's "the one that got away" and you just want to stay. How much of this emotional ebb and flow are you aware of?
Please don't think you're supposed to rate my response and pay me already. I'm just starting a conversation with you that's meant to allow you to dig deeper into the facts and feelings in your situation. That's the collaboration between us that can lead to discovering what you can think, feel and do about your situation to move forward with your life, and to move toward what you can achieve. You may not be able to bend your boyfriend to satisfy your desires, given the other people all pulling on him too. But you can choose your own path and gain for yourself what your situation offers to you.
I've reread what you've already tried. Those that study the biology of humans and other animals call jealousy "Mateguarding," because it is what any person would do in your situation. Your HEAD (which is "educated" by social customs) is pulling on a leash that drags your HEART off of its instinctual path into a swamp that would soon become QUICKSAND of depression if you did not struggle against that leash that's strangling your BETTER INSTINCTS. For the intellect is capable of being PERVERTED by false lessons from the SHEEPISH CROWD: You can't BE NICE to your BOYfriend! (accent on the BOY, because he's BEING NICE to several people he's known a lot longer than he's known you, and they're all following THEIR HEARTS.
YOU and HE each have a tug-of-war going on between your HEADS and your HEARTS. I have to go now. Please respond to what I've written, and I'll get back to you later today. Don't rate me and go away: You need to face the fact that your HEAD has learned (quite normally, because this NICE SOCIETAL LEASH on our hearts is what upbringing and social beliefs are for) to strangle your HEART. Now you have to make NEW decisions related to that problem. Tough decisions.