I'm suicidal... why haven't I killed myself yet?

I've suffered from general anxiety disorder since grade school, depression since late middle school, was molested by my younger brother in 9th grade, started cutting at 17 but have only done so once in the past year and a half... though I seriously wish I'd allow myself to cut more often. Have an okay job for now, but I'm graduating college in a few months and I won't even be 20 yet... I want to go to grad school, but can't afford to get into debt. I am taking 22 hours currently. I'm tired all the time. I just wish I could slip into a coma for a month or so to recharge my batteries. I don't want to move back home after finishing school because I'm expected to be a third parent in my household and home is generally incredibly stressful and not a healthy place for me to be. My parents know nothing of what I type here, save some about school, and would only blame themselves if they did know. I generally hate myself and have come up with many ways by which I could kill myself. I claim Christianity, though my faith is not something I flaunt. I generally feel that all good things are meant for anyone but me and I'm not worth any effort what-so-ever. Why do I bother.