It was a mistake.

I understand he was drunk and trust that it lowered his inhibitions and he made the wrong decision to sleep with her.

I believe he is telling the truth and it did happen before we started talking and dating again.

I can trust that he is telling the truth.

You’ve done some great work reflecting on this situation. I hope you don’t mind I copied some of your quotes. I don’t know if this suggestion will be helpful at all. I would suggest writing these quotes down for you to read when you are feeling anxious. It’s something my therapist taught me and I’ve found it helpful myself. If you would prefer feel free to select your own quotes or add to it. I thought these realisations were particularly profound.