Found things in my Fiancé's phone - what to do?

My fiancé (M19) and I (F18) have been together for two years and some change now, engaged for about four months. We decided to room together at college and we had a rough adjustment period. Things got blown out of proportion pretty quickly, but I think we were just stressed overall and he doesn't emotionally regulate very well. Early November we had an argument and he got really mad, went to another room for awhile and came back chipper, telling me that he loves me and asking what was wrong. We had a conversation that didn't go great and I just knew something was wrong, so I checked his phone. When I did I found 1) messages between him and his buddy and 2) a ChatGPT thread. In the messages between him and his buddy he said: I think I'm going to tell her we need to take a break, I came home late and she's mad, if she says anything I'm leaving (the room), I might sleep at [finance building at our university] I don't want be next to her right now, I feel bad I want to apologize, I just miss how things used to be when we weren't always fighting and I actually enjoyed spending time with her, he doesn't think it can be fixed. The ChatGPT thread was really long and much meaner, so to summarize, it said: How do I know when a relationship is over?, our relationship history, he feels like he's holding on to memories, he thinks he might stick this next semester out and then just stop hanging out with me/initiating things with me as much (important to note that he slept with me that night, wtf), he doesn't care for couples therapy or having a long conversation, he doesn't know if he wants to fix it, he's just a guy in college and wants to hang out with his friends and do his homework when he wants. The time frame for all of these messages would have been between right before he left our room and right before he came back. I was absolutely heartbroken and so infuriated because all of that just reeks of immaturity. But here's the thing, after this, we've gone nearly completely back to how things used to be between us (perfect) before we got here. He makes time for me, we laugh together, and actually have fun now. Here's a strange detail though, I went back to take pictures later, and he deleted the ChatGPT thread, but not the messages with his buddy. Why? If he was concerned that I would see it wouldn't he delete both? I plan to tell him when we get on winter break and we're at home (we're 4 hours away now). But what am I supposed to do? I truly love him so much and I can't imagine my life or future without him. I thought he loved me the same way, and maybe he does? I'm having a hard time allowing those two versions of him to coexist. I knew he was capable of getting really mad before, at his parents, strangers, etc. but it's never been directed at me before. What do you all think of this? Was he just venting and saying horrible things? I would never say things like that about him. Any tips for when I tell him? I really just need any thoughts because I'm lost at this point.