Tell him I'm actually asexual and every moment he's touched me for the last year has made me feel dirty and I cry at night thinking about it.
I have a feeling he won't want to go near me after that.
On a more serious note
That One Six said:
I haven't ruined my sex life yet, but in six months, I've only managed to get her to climax once, so my self esteem is kind of non-existent by the time I finish, and I feel kind of worthless afterwards. If anything, this is what's gonna screw me over.
Firstly, some girls just aren't very good at climaxing. The female body is a weird thing. Does she have difficulties bringing herself to orgasm when she masturbates? If so, then it's certainly not your fault and you need to stop beating yourself up.
If she doesn't masturbate, this may be the problem, she needs to loosen up about her sexuality!
Secondly, if it's not her weird female body that's the problem, then have you got her to teach you what she likes? Get her to guide you in foreplay, tell her to move your hands where she wants them, let her take control.
In my experience, guys don't make a girl orgasm, a girl has to use a guy to orgasm.
(P.S. Any questions asked are more for your consideration than to find out the answers. Advice post end.)