UCLApremed:
I know there are many things to be considered here. But from what yiu described, do not be around people (especially lovers)that makes you feel "crap". I passed through this myself, I was happy when I was with others. I was the "worst person" when I was with her. I did not listen to my own heart. I even married her. We have not so good time together now 3 years in our marriage. But now I am stuck because we have a 9 months old beautiful little girl. And I don't intend to divorce for my baby's sake. What I mean is we will try to work it out. I believe in commitment. I hate divorce. I don't mean it will never happen if the situation grows to be like hell.
But back to your situation: It is nice to have problems and to learn to overcome them during courtship. But through it all there has to be a love, a bond that pulls you together. If there is true love, your gf will think you can do any thing.... At least my wife supports me in my aspiration to become a doctor. You are not married, if you are not happy about her now, I don't think you will be happy after you are married with her.... I hope you understand me.
If you break up now, it will cause a temporary hurt, but if you keep going like this and marry her, it will cause a much greater hurt, for both of you.
Good luck.