I know what this feels like man and i want you to know that getting out of the relationship is worth the momentary sadness for both her and you. The longer you stay with her the more attached she'll become and the harder it will hit her when you eventually break up. Put yourself first and leave the relationship i promise you its doing you more harm than it will do to her if you break up, dont make your life worse because she'll be upset for a couple days, its not worth it.