Since you asked.
You have been wonderfully honest about the struggles you experience in finding positive relationships (whether friendships or romances). You've talked a bit about your tendency to allow people into your life who don't treat you well. This is a habit that you have, for very understandable reasons, developed over the course of your lifetime. Like all habits, simply understanding that they don't serve us well isn't enough to stop them.
My view on romantic relationships is that they are particularly difficult in this regard because of the way lots of people in the West are socialised. We are taught from a very young age that romantic relationships should be difficult. There should be an adversity to overcome before the lovers can live "happily ever after." It starts in childhood with fairy tales and goes on into adulthood as the plot of many books and films. So the notion of being parted painfully and then dramatically coming back together is, I think, embedded in many people's mind as a model for how relationships should be.
Sex, in my opinion, makes this tendency stronger. Sex floods our bodies with mind altering chemicals. Some of that just makes us crave more of it. Some of it is about bonding with the person we've just had sex with.
In light of all of that, I'm not surprised that you are finding it difficult to move on from this relationship.
But to me, your 'ex' doesn't sound like a good person to be having a relationship with. I have no doubt that he is a lovely guy with many wonderful qualities. None of that makes him a good prospect for being a supportive and compassionate friend or lover.
The red flags for me are:
1. He has shown that he is willing to lie to and cheat on somebody who he has a significant relationship with (his wife). So there is pretty strong evidence that he is likely to lie and cheat to get things that he wants. Not good traits for friends or lovers IMO.
2. He is unable to take no for an answer. You have asked him to stop contacting you and he is refusing to do that. For me, this is a red flag of massive proportions. Your 'ex' is showing you repeatedly that he will not listen to you. What you want doesn't matter and isn't relevant to him.
I doubt if he's doing it deliberately to be horrible but he is doing it. His motivation isn't relevant, his actions are.
For the moment, you guys aren't even really friends and he still can't listen to you. I can only imagine that will get a lot worse if you restart a friendship or a sexual relationship with him.
From what you've written, the fact that you are even thinking about seeing somebody who has repeatedly shown such poor behaviour toward his friends and loves, makes it look to me as if this is just part of your lifelong habit of allowing people into your life who treat you badly.
If I were you, I would continue with ignoring him totally. And concentrate on finding other interests to spend time and energy on.
I wish you well,