So my sister and I have always been best friends. We're a year and a half apart in age so naturally we've always been very close. This year, she started college at the same school as me, she's only a freshman this year. She immediately got in with some bad people. She was going out to parties every night and showing up to classes hung over. I'm not into partying much but I went with her a couple of times to a party or a club. I was totally disgusted to watch her grind with a buch of old guys and make out with a few as well. All in the same night. One of the guys she met at a club, she's been taking to for a few months now. I can't stand it. This guy is way older than her, he said he's in town to get some retirement papers as he was recently deported to Japan for the military. For that reason, apparently, he has two phones. Everything about him is just very suspicious to me. I also heard her on the phone with him, about 2 weeks after they first met, and she was telling him how much she loves him. I know my sister has always been pretty naive but she won't listen to me about this guy. With how much she has changed and with all the things she's currently doing that I cannot support, I can't see us being friends anymore. Just sisters. I'm also debating telling my parents about what's going on with her since she won't listen to me. They had instilled a bunch of rules for her after finding out about her partying habits, and she hasn't followed a single one. This is tearing me apart and I really don't know what to do because I hate her so much, but she's my sister.