I am currently going through something vaguely similar, though the men never cheat on me. My think is that I seem to attract men who are emotionally unavailable to some extent, who all like me a lot but at a point they back off and/or bolt. Even when I've been in a serious relationship, they will withhold affection to the point that I feel like I'm pushing and nagging just to get my needs met. I just broke something off with a man with whom I felt that same pattern beginning. And I have been doing some reading and it turns out I have a degree of emotional unavailability as well, and just like in real life chemistry, like attracts like. But my unavailability is a fear of rejection, while I'm attracting men with a fear of engulfment. So I eventually get needy and come on too strong and that's when they retreat. I don't know if this is what is happening in your relationships--women retreat in totally different ways than men (and I feel like women would have the rejection thing more than the engulfment thing, but it's definitely not gendered).

I bookmarked this link. Maybe it will give some insight, I don't know. But it is worth a read:
Why Do I Keep Attracting Unavailable People?