Dr. Mark has done a good job of describing the general problems of the type you began your question with. But your present elaboration points to more specific issues than the general ones Mark approached. I've studied some patterns in the series of relationships that people can engage in over what sounds here like 40 years. If your loverman is just excusing his sexual affairs by saying "she hurt me first!" then Mark's approach is still very useful.
But if he really did just start splitting sex off from love when his wife denied him sex, instead of divorcing her then, have you asked him WHY he stayed? Could be children, but it also could be a paradoxical kind of love that actually thrives on adversity, because some elements of intimacy DID occur, intermittently perhaps, but because of that all the more INTENSE when that intimacy was there. It's neat, but oversimplified to assume there are only 2 types of intimacy, sexual and emotional. For in fact there can be intellectual, work-collaborativeco-parental, creative/artistic, spiritual, crisis (facing outside challenges together, like with a suffering child), conflict (like fighting and then making up)--and some combination of these could created an emotional pattern that kept them together through thick and thin.
And the point of this possibility is that even if it was an unhealthy pattern, it could have been the most powerful bonding that either of them had ever had--even to this day. So he might have not ever gotten over the unusual intensity he had with his exwife, which could have made him both cheat on later partners and lose interest in them after the early passion (1-3yrs) had subsided. Bottom line, he's either addicted to the mix&match 2 partners solution to his personal needs, or he's not over whatever got him stuck in the first great love for 28 yrs.
Waiting 5 to 10 yrs to marry sounds ridiculous on the face of it; and it implies that he still has some attachments to exwife and/or past habits that he blithely assumes he'll need that long to get behind him. Or he's become a narcissistic lover who schemes to get himself 5-10 years guilt-free tryout period with each woman he wants, so he's well covered well beyond the 3 yrs it normally takes to wear out sexual passion with any one person (unless you're hooked on trying to turn uncertainty into security and chasing the one who keeps getting away). IT'S A BIG LOVE TRAP TO CHASE THE CHALLENGE OF TAMING THIS "WILD MAN."
So Mark is right, and I would throw the challenge back at him that you're now tempted to swallow hook-line&sinker yourself: Your challenge to him would be: I'll quit you NOW unless you carefully search out a very well-trained therapist and commit to working for at least 2 years. And that means seeking out psychodynamic (postFreudian&Jungian&other Unconscious-dynamics training and practice), not problem-focused or cognitive but long-term & personality-change focused, and old enough & with enough personal experience in therapy and as therapist to be impossible for the likes of him to fool.
Look up the 9 personality characteristics of Narcissistic Personality Disorder and count how many he seems to have--on the off-chance that he's not the victim of his exwife's frigidity but the perpetrator of multiple user-affairs. If he does have NPD, and is a liar also, then he won't embrace the challenge of working in therapy for change.
And I don't think that couples therapy is what you need with him. For unless the couples therapist is highly trained in psychodynamics and diagnosis and/or in Emotionally Focused Couples Therapy and readily consults with colleagues who know NPD and psychodynamics too, you'll be spinning your wheels trying to "win him away from all the rest" and he won't need to change. HE needs individual deep psychological work for personality change.
But if he won't take YOUR challenge, then you can leave him earlier than he's ready to dump you after wearing out his welcome. And you might be able to move on without as many scars on your self-esteem as if you'd stayed another year or two.
How much younger than he is are you? Is he so talented and successful that you are excited to be the woman that he (now) wants? Have many other of his partners been 10+ years younger too? That's a sure sign he's into predatory affairs in which he looks to himself and his prey like a much more accomplished person she'd admire. And that's exactly what a narcissistic partner needs.