What do I do

My boyfriend is at work and I logged into his snap bc he asked me to send his streaks. And I was scrolling just to see how many people he has on it since the last time i logged on. I found one where he was left on open by another girl so I clicked on it I scrolled up ik it sounds dumb but he said "oh hey btw your pretty cute" but bc of my past I had to ask him abt it and he said it was his friend who did his streaks one night because he was drunk. The drunk part I believe but idk abt the other part I want to believe him so bad and part of me does bc I know hes not like that but trust issues from the past came flooding back to me. I just dont know what to do. I trust him more than anything and hes allowed to have other friends that are girls that I'm comfortable with. But this one not really one of his friends but has a streak with. I don't want to leave him and I want to believe him but I just dont know. Does anybody else struggle w things like this?