I need advice... or just opinions

Hi, I identify as a biromantic demisexual and if I ever had a doubt about my demisexuality, I confirmed I was, in fact a demisexual last saturday.

Last saturday I went to rave with my best friend (a girl, lets call her Mary, with whom I had a short lived relationship some years ago) and her friend, that I'd just met 2 days earlier (let's call this one Jo).
So we go to this rave, the 3 of us girls, and we get high on MDMA (I'd never done mdma before, my best friend talked me into it) and Jo starts coming on to me, asking for a kiss, to which, I initally refuse, because I wasn't attracted to her, not even a little (for heaven's sake, I'd just known this girl for 2 days, and I'm really shy so I didn't get to know her like at all.)
The rave goes on, and she asks to kiss me again and I don't refuse and we make out. But it didn't feel right in my head; I won't lie, I was aroused, but it didn't feel good in my head, I don't know how to put it in words exactly, but that's how I felt. Then she started to grind against me, touching me and licking me and by then she asked to have sex with me (we didn't).
Until now, I feel like vomiting whenever I remember all of this. I cringe when I remember how she touched me and I really wish I could forget that night.

Right now, I just really can't stand my own skin.

has this happened to any of you? I'd feel better if I knew other people have felt like that before.

Oh, first of all I'm sorry to read what happened to you :/ Luckily you didn't have sex (against your will)... :/
And yeah, I could say I can relate to this in some sort.. I mean, I was confused, I had a really ugly break-up with my first (and very strong) love, I couldn't forget it and didn't manage to move on. 7 years seemed a lot longer than "common" single phase after a break up.. I mean, my friends moved on much earlier than that so, well, I wanted to try to "build" love attraction. So I made out with friends I loved very much, trying to convince me love had to be built some way and maybe having sex was it (well, it seems to work that way for many people, in real life, in movies, everywhere, why not with me ?!).
So I had sex. And yeah I was kind of aroused, but I think it was purely "mechanical". My body was aroused, but my mind was... not so good. I had to put an end to it (I was stupid enough to try that strategy two times) and told my friends that I couldn't keep going like that because I just wasn't in love with them and it felt soooo wrong in myself. I was ashamed after sex, I felt like I'd been used, but not by them. By myself. It wasn't worst, but in a sense, it was, since I was responsible for having let that happen. But well.
One of those friend told me one day I was like this character in the tvshow Heroes. The one with 2 personalities. One time I was aroused and ok, and two seconds after I was angry and almost violent verbally, or totally back into my shell...
My stomach ached when I thought about it, I felt horrible. I guess that's the closest thing to rape I have felt. (I've never been rape and can't imagine what it's like, and won't compare it in any way, but I think that's the closest I felt.)

Now, all of this is far behind me, and I take that as a (quite hard) way to learn about myself and how I work. I didn't know about the term "demi-sexuality/romantism" (I put the two in one because commonly when people say they're homo/hetero/bi/pan-sexual, they mean in fact both "romantic and sexual" attraction ).

I don't know if it makes you feel better. I don't even know if you think my testimony is on the same page as yours.. I hope you're friendship won't suffer from it, people tend to act weirdly under the influence but well.. :/

I appreaciate you replying a lot. I'm glad I'm not the only one not feeling good in my brain while being physically aroused.
I'm better now, i got a chance to discuss what happened with a friend and it somehow made it all better.
I guess it'll take me some time to put what happened behind me and I'm glad that as you said, I didn't end up having sex with that girl (this would be about 10 times worse if I had)