Boyfriend kissed someone

So my boyfriend told me he kissed someone last week because he went out and had a few too many drinks and went home with a girl and kissed her. He didn’t have sex with her or anything and left before anything else happened. He apologised a lot and promised me he wouldn’t do it again and regretted it, we talked it out over the phone and I forgave him easily and I don’t know if that’s good or bad but I’m still pretty pissed and I lost a lot of trust in him. We have been talking like we usually have and I don’t know what to do, still bring up about him kissing someone else if I feel unsure or sad or just leave it but he’s trying to make it up to me and I feel normal ??? Idk I don’t know how to react