Boyfriend doesn’t care and thinks I cheated

On New Year’s Day after coming home from my boyfriends I was hungover and sleeping in my room. My neighbor stopped by and my mom let him in and yelled from the living that he wanted to see me. I said no idc I’m sleeping. He came into my room and grabbed my butt and immediately sat up and he tried grabbing my boob and than he was whispering for me to come downstairs with him. I told him no and to get away from me. He eventually left. I told my boyfriend after it happened. Now 4 months later he brought it up in a fight because he doesn’t trust me (never ever gave him a reason to think I would cheat) I would never cheat anyway.

I don’t understand why he thinks I would be with other guys? I don’t talk to anybody. I don’t even have girl friends. I’ve never talked to anyone else since being with him. Also really makes me upset that he is blaming me for having some random dude grope me and not even caring or being mad at the guy but turns it on me. I was in a smelly t shirt and leggings in my own damn room but somehow that’s putting myself out there? He doesn’t trust me but never once asked to see my phone to check my messages which I would gladly show him cause I have nothing to hide.