I (19F) and him (20M) live together. We were at home together one night hanging out with a friend of ours. We'll call her Sam (17F) (not her real name but for privacy purposes we are going with a fake one). We were all hanging out one night and watching a movie. Some drinking happened earlier in the night because we are all stupid teenagers and wanted to have some fun.

As the night went on, everyone became sober and all 3 of us sat down to watch a movie. I had a migraine from the drinking and I told my fiance I was going to bed so I could get rid of the headache. Not to long after I went and laid down, I fell asleep.

The next morning I woke up and didn't know where my phone was so I grabbed my fiances to check the time. I had seen he had notifications so I decided to see if any were important. I wasn't going through his phone, it's just something I normally do because he hates having a bunch of notifications that aren't important on his phone.

Anyways, I went to go swipe them away for him and realized that someone I had went to high school with, had followed him on Instagram. I was just curious to see if it was actually the person I thought it was. I had saw he had messages and at this point I was just curious and also had a weird gut feeling.

I checked his messages and saw he had been texting Sam. Which i was confused about because the last message had been from a couple hours ago. I was confused because well, why would they need to text if they were right next to each other? So opened the messages and looked through them.

I was disgusted and broken by what I saw. There was multiple long messages from my fiance to Sam of many sexual things. I'm not going into to much detail about it but the messages were very detailed. I read through them a little and I woke him up afterwards. I asked him what the messages were about and he didn't really give me an answer. He just told me he doesn't remember because he was drunk.

Things don't add up much because of the fact that there wasn't anymore alcohol before I went to bed. Also, we were all sober when I went to bed as well. Apparently, neither Sam or my fiance can remember anything that happened the night before. I can't seem to shake the feeling that more happened then those messages. I have told him I forgive him but I don't.

So, AITA for not forgiving him? Should I forget about it and just move on?