Hey vampyre love,
Sorry this one got over-looked...
These types of parties always get out of hand. You described it well to say it was shocking. It sounds like I don't have to tell you how dangerous they can be. The thing that is hard to understand is that the bad thing, whatever it is - can happen
in an instant. When alcohol is involved, its like going up to your car, putting on a blindfold, getting in, getting behind the wheel and driving away while totally blindfolded. It can have serious consequences. So the best thing you can say to yourself is "you know what? I'm not going to go there and put my life in danger. If you do go,
don't drink and leave early. The best thing is just not to go.
As for talking to your T, it sounds like it could be really helpful. Maybe you could simply ask her for some ways to address what to do if you were invited to that kind of party (without mentioning that you were unfortunate to have to go through it already) ask how you can keep your respect and just say a very strong "no thanks." I hope you will. It means you would be taking care of yourself. It is
really not worth it to get involved with the parties and major alcohol. It means the police, it means a record, it means alcohol poisoning, it means pregnancy, STD's, rape, regrets. Nothing (and I mean nothing) good comes 'em. I urge you not to bother with it... There are honestly so many more fun times to be had. If you want I can name say, 15 better things to do.

Trust yourself, have faith, please take good care of you.