Not sure how to feel

[Ruefal]

Went to a fairly low key gathering on New Year's Eve with several of my mates as well as a few others I didn't really know. My friend recently picked up a girl from a bar (I'm 19, he's 23 and the girl he is with was 31), she clearly has some issues but he has some confidence issues and was just really enjoying the attention and the sex (she's been staying with him for a few days). She was very flirtatious towards me upon arrival. I'm quite talkative especially when a bit drunk so I didn't think much of it as I was talking to just about everyone.

 

Some time after midnight my friend went back inside and the girl asked me to sit next to her because she couldn't hear me (shed started a conversation about something I can't remember so it wasn't weird at this point). Soon after she leaned in and started kissing me out of nowhere, I was completely caught of guard, I pulled away at first and she went in again and I think I kissed her for a few seconds, unfortunately everyone saw this part happen and so it looked like I was at fault, I'm personally not too sure, I know I should have pulled away immediately but I suppose I was a little flattered as I'm more of a relationship person and I'm not used to random/drunk hook ups so much.

 

My friend came out just afterwards and at first he didn't know what to think but I reassured him, she proved to be a bit of a nutcase and tried to come onto me again while he was inside but I left the room and told her to go away. The mood wasn't really the same after that, a couple of dudes with girlfriends gave me the cold shoulder so I could only really talk to my friends, I left soon after, let me point out I was very drunk, it all happened in a bit of a flash.

 

It's no longer a topic amongst us as everyone agreed she has some issues and he needs to cut her loose but I still feel terrible and undeserving of anyone else after this happening? Should I be feeling this bad and is there anything I can do to make things better?