<human>: This sounds so childish and menial compared to some of the stuff on here, but it's burning a hole in my stomach.

So I met this girl through my flatmate, and we sort of flirted for a while but didn't think the other one was really interested. Turned out we both were, just had to get drunk to realise it.

Month on and we're hanging out a lot, seem to be enjoying each other's company. Feels a little strange to me as there's very little physical stuff, the only proper kisses were that one time when we were both pretty pissed. Bit unusual but fine, I'm happy to take it slow, assuming that's what she wants.

Then two days ago, I get drunk with a flatmate, and somehow we end up making out in my bed, a lot. She's stays the night (no sex) and then we wake up feeling like horrible people, then make out some more, cause we are horrible people. But it was really great, and I felt something that wasn't there with my (sort of) girlfriend. Essentially I realised I had feelings for this girl that I'd repressed since she's a flatmate and I thought it was a bad idea to go there, and now I knew she felt the same way and I couldn't really ignore it any more.

I know I have to tell the girlfriend, I'm just unsure how to sort out this whole mess with minimum problems/hatred towards anyone. I think I want to break it off with her as well, we weren't having as much fun as I thought we would.

Can you condense the text into three sentences or less?
<bot>: How do I break up a short term relationship with a girl because I like her best friend, without creating huge amounts of drama or unnecessary pain?