Long Distance Relationship Problems NEED HELP!

I have been dating this girl for 3 months now. We are both 18 and she is going to college in New Orleans and I'm going to college up here in New York. She lived here for 2 months and left right in the middle of August and ever since then it has been really rough. It's like she goes out on the weekends, is drinking alcohol, tried pot once which got me really upset and we got into a huge discussion about it, and staying out really late and barely is able to talk to me on the phone the next day. While she was here, when we were around friends, she NEVER did any drinking or smoking, didn't even mention it. Now I think she is changing on me, she says she loves me with all her heart and I love her to with all of mine, but I really don't know what to do at this point. Last night I got upset because she said she was having a couple of guys over in her dorm, one of them was her roommate's boyfriend, and I got upset because we always talk to each other at night, and she didn't understand why I got upset. Can somebody please help me out there. Tweet