He left yesterday and is coming back on Sunday. He’s staying in an apartment with 4 other guys and one of the guy’s girlfriend. The girlfriend happens to be a nerdy, attention seeking redhead who used to flirt with every single guy in their old groupchat. She’s the reason why my boyfriend doesn’t see them anymore and even though her boyfriend is there, I am absolutely terrified that something bad is going to happen.        
My boyfriend keeps reassuring me that he loves me and that he’s not going to cheat or leave me, but he’s already snapped a few times and told me to fuck off. I keep finding loopholes in everything he says to me and I strongly believe that he doesn’t love me and won’t be coming back.       
I have nothing but dark thoughts running through my head and I can’t stop them. I feel like there’s another voice in my head telling me all these ugly things about myself and I can’t stop it. I try so hard to resist it, to focus on something else, but it’s almost obsessive at this point.      
I feel like I can’t enjoy anything, even though I knew this trip was coming up and I tried to prepare myself - made plans, bought myself a journal, made a happy playlist, downloaded some games and started reading a new book. But I can’t do any of those things, I feel like I’m paralysed and the only thing I can think about is him cheating and leaving.     
Sometimes I feel numb for a few minutes and that’s the only time when I can breathe properly, when it doesn’t hurt.         
I don’t know what to do. I’m not officially diagnosed, so I don’t even know if I’m posting in the right place.