Did I make the right decision?- college and friends?

I'm a college student and I had this really good friend. I've always told I am more mature then people my age. I have been with a boyfriend from home for 2 years now (and I'm a sopre in school). He's 4 years older then me and as of know we are so in love. My boyfriend's past long relationship ended back with her cheating, so I am really against it. My friend has a boyfriend at home and they have been dating for 4 years Well everyone was drinking and having a good time two weeks at school (the only 2 weekends she spent at school this year).. the first weekend I stayed up until 5 am with her as shes crying that she didn't "get with" any guys that night as I was telling her to stay true with her bf. She went on and said that I was a good friend, and that I was right. Well the next weekend at school we go to the dance and goes off with our roommates friends and then when i asked her to dance with me she said eww get away i want to dance with a guy not you. So I ended up leaving with my friends without her. Well when i went out to the eat at one place around my campus with them. when I got into my building my other friend who was working at the front desk told me that she couldn't walk and was being pulled by a "description" guy I went online found the kid's name and went to go look for her. I asked around and repeatedly called her when I found his room I saw 2 guys and asked if my roommate was in there i threatened them a little bit and they said no.. well i gave up and came back to my room almost an hour later. my other roommate gets a text saying shes on her way back, but I was the one who called her 20 times looking for her I feel pissed because she didn't care to tell me as she came back i let my other roommate take care of her and put her in the shower, after my roommate said make sure shes ok i'm leaving. she was in the room where i asked for her and she had hickeys all over her neck and her "vigina" hurt. after hanging out with this kid the next week and hanging out with him till really late again bothered me because her bf doesn't know about him, i felt uncomfortable knowing this is the 2nd time she cheated on him. well she turned 21 this week and let her bf take her out, then goes and hangs out with the other guy, she's been telling my other roommate everything, despite the fact that her and i were closer.. as they were partying in my room on her birthday (there was a lot of underagers I don't like) i felt uncomfortable i went to one of my ras who is my friend in the building and told them he went to go talk to them while i went to study with someone else. well i ended up texting her saying that she's changed and it doesn't seem like she wants to be my friend anymore, so when she changes back to her normal self. now someone who was in the room on her birthday drinking asked if i called public safety, i didn't call so i denied it. I know I have other good and better friends but i still feel left out and lonely in my own room, I really need and want to focus on my finals this week, but it's hard not thinking about how everyone hates me. did i do the right thing, should i fix anything- if so how, and do you have any advice to keep me focused and not upset that i miss my how my friend used to be