Thanks for the responses, guys. I apologize for making my original post so vague, ha. I think I do know why I am attracted to her (we are both females), but I don't think it's because she is unattainable. She is basically one of my only friends, and the only good friend that I have had in a long time. So, she's pretty much one of my only sources of general warm feelings and physical contact, which are things that I really crave. So, as sad as it sounds, I think I'm crushing on her because I can't really find love anywhere else.
My feelings more or less came out of nowhere- one second, I was really glad to have her as a friend, and the next, I'm feeling like I'm falling in love with her. The issue here is that I really do let this consume me too much. I've been more angsty and pessimistic than usual about my love life lately, and have been losing sleep dwelling on the fact that something between us would be utterly impossible. I also have a bad case of that needy "I don't want to text her because I don't want to be annoying" thing. I spend a lot of time browsing articles online so I could send her one pertinent to her interests, just for an excuse to message her (because everyone loves receiving cool articles, right?).
Anyway, the whole thing's just got me really down.