Most Helpful Girl
In my opinion, good on you, sure the occasional hot sex from an ex can be nice, but I'm pretty sure that the fact that you didn't take advantage while she was drunk shows good on your part, and I don't think your girlfriend would have liked it if you did. But here's the thing, if you're still there, you should probably leave, you made sure that she made it home safe and everything, but by staying will only result in your current girlfriend feeling possibly insecure and worried about you. You did the right thing, now let her get over her hangover and get out of there.
Most Helpful Guy
If you already have a girlfriend, either get her involved (maybe drunk girl is bi) or if you care about your relationship then leave a note and go home.