She's just so freaking selfish and it's driving me crazy. We have an online assignment due before midnight tonight and she just texted me asking if I'd done it and if she could get the answers from me when she gets back tonight. I'm pissed because it's a freaking long assignment and took me two hours to finish. And I'm supposed to just give the answers to her?

She also wants me to go with her to park her car on west campus. We're allowed to park our cars wherever we want over the weekend, but once the week starts again they have to go back to west campus, which is a freezing fifteen minute walk away from main campus, where we live. She expects me to go with her, yet every time I've had to take my car over there she's too busy to go with me.

So instead of being the good roommate as I've always been and give her the answers and make that freezing walk with her, I texted her back and told her I had mandatory library hours for one of my classes. So now I'm hiding out here and getting my own stuff done instead of putting myself out for her. I feel kind of guilty because I've always been a good roommate, but it's gotten to the point where she's just using me and she's never done shit for me. Am I a bad person for avoiding her?

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We had some massive nights
Every song was right
And all I wanted was time

I'm thinking that making her take responsibility over her assignment tonight is the best thing you can do. If there's going to be any conflict over this, it should be between her decisions, not between you two. So just stay at the library until she figures out what it took to do the assignment on her own. She won't have anyone to blame but herself.

You are being used and unless you want it to stop you need to have a really heart to heart conversation with her.  I would suggest that you start off telling her how important she has been but things have changed and you don't feel like the feeling is mutual anymore.  State what is acceptable to you and what is not.  

I think you should probably talk to her and see why she thinks that she has to treat you this way.  Tell her that she always expects you to do things for her, when she never does anything for you.  Now this may make things hostel between the both of you, as I know many girls don't like when people tell them the truth about themselves, but you need to get it out before what she is doing affects your school work. Believe it or not, friendship stress can cause you to slack on your work, especially in the case where she isn't doing anything and just wants you to do her work for her.

So just try and have a civil conversation. Try not to get riled up, because if you both start getting angry and yelling you aren't going to get anywhere.

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I need to run away to find out who I am.
I need to stay and face what I've become.