<human>: Give me the gist of the text in a nutshell

Okay, so first of all: I'm going into my senior year of high school and I've been with this girl since halfway through Sophomore year. For the most part, it's been a happy relationship. 

But lately, I've found myself to be less and less happy in this relationship. It's extremely draining emotionally, and I don't know what to do. I certainly don't want to spend my last year of high school being unhappy. I love her and I definitely see the good in her, but there's too much for me to handle.

She's EXTREMELY emotionally dependent on me. I'm the one person who she talks to about her problems, and while I'm very willing to listen and be there for her, I can't handle all of it. It's just too much for me. I'm afraid if I break it off then she won't handle it well at all. I couldn't live with myself if something ever happened to her. I don't know if this makes me sound like an asshole, but I don't know what else to do.

I've kind of rambled on in this post, I hope it makes sense. She's constantly unhappy, and I'm the only person she can go to. Frankly, I'm afraid of how she would handle it. I need help, I don't know what to do. Am I a selfish asshole for this?

She takes out all her anger on me, and is mean to me and makes fun of me in a non-playful way pretty much ever day. My feelings aren't considered most of the time. She always realizes this and apologizes, but it still goes on. I don't want to be with someone who acts like that towards me.
<bot>: Girlfriend is extremely emotionally attached, if I end it she will not handle it well. I can't handle the emotional anguish anymore.