Hi reddit, I'm a long time lurker and first time poster.

Last night I was at an acquaintances birthday party (lets call her A). We've known each other for several years and there have been intermittent sparks and some making out but nothing beyond that. We both travel a lot and live a fair distance apart so nothing serious has really had a chance to develop. Despite this I am rather interested in hooking up and perhaps starting a relationship with her at some point in the future.

Now at this party, I met A's friend (lets call her B). B is not as attractive as A, and while A is generally very self confident and gets a lot of male attention despite not being super hot (we're all a bunch of nerds) so A likely thinks of herself as a 7.5, B is maybe a 5 or a 6 with confidence issues. I had good interactions with almost everybody at the party and things went fairly well. About half way through, B came over to sit by me and started falling asleep on my shoulder. I took her into a bedroom, we made out and were about to have sex when I got some weak LMR, and reconsidered. I put her to sleep and returned to the party.

Later on in the night B came back out and was understandably uncomfortable around me. I had little interest in B, so it didn't really bother me.

Once the party wound down, B left and I (being not sober enough to drive) went to crash on an empty bed. A couple of minutes later A knocked on my door and came in to talk. We ended up cuddling on the bed (I possibly had an opportunity to make something happen here, but didn't want to risk damaging my long term prospects). She passed out quickly and started snoring so I woke her up and she went to sleep in her room.

Now B want's to meet up and it seems pretty clear that she wants my dick. I wouldn't mind breaking my recent dry streak, but I don't want to ruin my prospects with A.

tl;dr: would hooking up with a primary target's friend ruin my chances with her in the future?