So jumping right in, I generally struggle with confidence in talking to girls - even when drinking. I'll pull the classic, "another beer and maybe I'll feel like approaching" all the time and usually just end up way too drunk to do anything, let alone talk to girls. Last night, however, was different. I was killing the scene at my fraternity's first party since rush was over. Met lots of new sorority girls, approaching many of them myself (which I rarely convince myself to do). Danced with some girls, talked to some one on one and some in groups, and overall had a great time, while not getting too drunk to function. Eventually, I hit it off with one very cute girl and brought up to my room near the end of the night. We chatted for a bit, laughed a lot, eventually got to making out. She was pretty into it at this point, climbing on top of me. We stopped for a minute and I went to the bathroom to grab her a glass of water. Got back chatted a little more, figured it was time to escalate things to the bed, so I stepped out again to pee so I didn't have to worry about that later and when I returned, she was gone.

This has been totally fucking with my head, and after having more confidence than I ever had last night, that's all been completely shot. I have no idea what went wrong - she was super into me which was one of the real reasons I pursued her - she made it easy. I never got her number, don't remember her name (I wasn't that hammered, we just introduced ourselves the one time in the loud party and I had met a lot of different girls that night) and she's not in a sorority, so I don't even know who she was there with. Perhaps one of her friends needed her or she had some real reason to duck out, but I have no way to confirm that. Just looking for some advice on what possibly could've gone wrong and how to regain the confidence I had last night after getting it completely wiped away.