<human>: Condense the text into a few key points

I'm just looking for advice really. It's not a huge deal but it's bugging me and I just really need some advice on how to get over it. 

Basically my boyfriend is moving in with two girls. He's really close to one of them and they've had sex together previously. He says there's not really any attraction there but I mean, obviously there's a little if they've had sex, right? I'm just concerned that they might get drunk and cuddle which would then most likely lead to sex. They might not even get drunk. We could have a fight and he looks for comfort without thinking about it. I don't know. I don't have any reason I distrust him but I know what alcohol does to people and I know how hard it can be to control yourself when you're mad at someone. 

I really want to just let it go. Any advice would be appreciated at all.
<bot>: boyfriend moving in with a girl he's had sex with, I'm concerned something might happen which leads to them having sex again.