What do I do about my roommate?

my roommate and I have been friends since our junior year in high school, we ended up going to the same university and decided to live together in the dorms. After we got here I noticed a few changes in her. She starting dressing slutty and she even gave this guy the first week of us being here. she was not like this back at home. next, she started acting like her **** didn't stink, like she knew better than me. She starting walking around Greek row in the middle of the night looking for a party, I went with her because I didn't want anything bad to happen to her, but I felt like we were street walkers. she got a boyfriend who is from a Frat house and started spending the nights there, which I'm cool with, but then she joined a non-housed sorority and i barley see her anymore. for example the most I saw her this week was in our math cl we have together. I feel like I do so much for her. She doesn't have a car, so anytime she wants to use mine, I'm fine with it. But now I'm starting to not be okay with it. She will come from her bf house, stop in to change into work close, then just take my car without even saying so much as a thank you or even how has your day been? I am struggling with trying to be a good friend, because some might say that I should just treat her the same way, but that is not me. I am a good person and a good friend, I pride myself on that. Today, she really hurt my feelings. I grew up in a house where I shared everything with my sister, except football. That was something for just me and my dad. My dad is very ill and I am not sure how long her has left, but nevertheless, I take advantage of everyday I have with him. So today, My dad and I's favorite team was playing so I was watching it and we were texting backandforth since I couldn't go home to see the game. My roommate comes in to grab her stuff as usual and asks me what I am doing. I told her watching the Jets game. Her reply was, "of course." now I know that she doesn't like to watch football, she has made that apparent more than once, but i don't see how me watching football when she wasn't even there is such a burden to her. I let is roll off. and she puts her two cents in saying the Jets suck and she was rooting for the Steelers. This pissed me off because she doesn't care one ounce about any sport and she obviously was only saying this to hurt me. This i don't get. Yeah, it's just football. But this is the one thing that is just for me and my dad. Why would she try and hurt me like that? Even as she left the room she was yelling go steelers. A few weeks ago my dad was administered into the hospital, I was at school and had plans to go eat some lunch with my roommate went I heard the news. so I drove home and told her I was so sorry I couldn't make it. The day before my roommate was giving my a hard time about spending so much time with my dad. I had then replied i didn't know how long he was going to be here for. She told me to take it back and knock on wood. I didn't because I'm not supersticious. Then by utter conicidence i found out about my dad. When I told her I couldn't make it too lunch, her reply was, "you should have knocked on wood," not "is he okay." nope no comfort for her whatsoever. My suitmates and a girl across the hall all of whom I have only known for a couple months comforted me more than she did. So I don't know if i really have a question. i might just want comformation that I'm not over reacting and a chance to vent.