Hmmm..... I agree with Middlemarcher. It could be the straw the broke the camel's back. Thing is, he has cheated and blown up at you and has walked out several times. What's going on here? Is there more to the story given he has walked out before? Is it always about the cheating and your suspicions?

I would not feel comfortable myself marrying someone who has cheated on me, but you said you have tried to move past it. However, you both are not past it, and he is doing suspect things to boot.

Maybe some counseling will help. I wouldn't go begging him to marry you and get back together. Maybe sort things through for yourself first.... things can always be worked out, but it sounds like there are some issues here. Abandonment and trust issues. And then whether he is truly the right person to settle down with. I mean, if he keeps storming out and threatening to leave, pushing your buttons and triggering your abandonment issues, is he really the right one for you?