Am I overreacting to my boyfriend deleting people from his phone?
So I [25f] have been with this guy [29m] for 3 months when a week before this incident, we were having an argument. It was over the fact that when he talks to me about his past (in general), he never forgets to mention women from his past that he claims weren't right for him or cheated on him (blah blah blah). So I brought up that I'm not necessarily interested in hearing about his previous relationships like that and that I'm feeling quite uncertain about my place because of it, so to reassure me, he asked if "I would want to have a threesome and watch him fuck another girl". I (rightfully) got extremely upset and asked what would possess him to ask that? He claims it was a joke. I didnt find it funny one bit. We talked about it, he felt assured that it was dealt with. I wasn't.
I go to see him this time and I still have it in the back of my mind. We're in bed when he notices I'm overthinking so he asks me to tell him what's wrong. I say that because of what happened last week, I feel unsure of our relationship and that he isn't speaking to other people. He offers me to go through his phone (while I hate to admit it as someone who's never wanted to do that, that's exactly what I wanted), so I do. I go onto his snapchat and see that there are two random girls and so I ask him, "Who are these girls?". His response is to say no one, so I ask him to click on one of them where his message is still delivered and he refused. He starts going on about how he'll just delete them and its not a problem. I reiterated that its not okay and he wouldn't be hiding it if he thought so too. He ends up removing them (and therefore whatever was on there) which led to an argument (definitely mostly me) where I questioned and asked why would he delete them and not just show me. He says he panicked. I asked what the fuck he said to them. He said that he must've just replied to one of their stories. I said fuck that and was going to leave but it was 2am by that point and I was emotionally devastated.
I don’t know if I'm stupid or just trusted that he wouldn't do anything like that (again, he consistently brings up the fact that he was cheated on in his previous relationship). He says he deserves a second chance, but I don't see how I can physically give one when my trust and faith in him are completely gone. I don't know if I'm actually overreacting especially because I technically didn't see anything. I suppose, what do I do?
TLDR; My partner deleted people from his phone after I saw him messaging people, but didn't want me to see the message.