Help!

Ok so my boyfriend admitted to cheating on me a few months ago, he said it happened twice! I don’t know who the women was who he slept with, he says he was driving and saw her and they had sex in the car, but he said it happened more than once so that is bull shit to me, he’s either gone back to her house or something I’m not stupid, anyway I still haven’t forgiven him but I’m still with him after a break, I can’t get the fact out of my head that he slept with someone else and I don’t know if he’s doing it again, he says he’s not going to do it again but how can I trust him....I can’t and I’m so paranoid all the time! :(