<human>: Can you succinctly summarize the text in 1-3 sentences?

hey, internet, so, I've read quite a few of the "should I/how should I break up with my boyfriend/girlfriend?" posts and I'm kind of at a loss, here. My general attitude is that if you feel like you have to ask, it's probably time to move on, and it's been three pretty grueling years of me wondering, so I'm pretty sure it's time to move on. Most of the posts in the "should I?" vein involve the partner in question being pretty much textbook abusive, and neither of us are or ever have been. Infact it's gotten to the point that we're kind of like extremely civil roommates, who buy eachother stuff sometimes (but have not had sex in six months). 

My girlfriend is a sweet, infinitely caring, deeply compassionate person who has sacrificed a lot to be with me, and, though I try my best to support her, I've been kind of a scummy shithead to her. Beyond that, having thought pretty comprehensively about our history together, I can pretty objectively say I have been holding her back and have brought much more grief than I have brought joy to her life.

 So, how do I leave my girlfriend, 1) with whom I live, 2) who has done nothing wrong, 3) deserves INFINITELY better, 4) has tried very hard to make this work, 5) has pretty measly self-esteem and few friends, 6) do you need more?
<bot>: I tried to keep this brief, but, a very nice girl decided she liked me and I do not and have never liked her very much. How do I, after spending four years building a relationship with her, leave it?