Abuse can have lots of effects, some of which are unexpected to the person. It may be worth looking into with a therapist. I think, though, I can take a crack at your question.

When you cut, your brain releases endorphins. Endorphins give a sense of "well being" (Wikipedia...not the best source, I know, but stay with me here ) when introduced into the body. When hurt, such as when you cut, they're released to give you enough of a "boost" to get out of whatever situation you're in (speaking to the "fight or flight" response). It works quite like gunshot victims not knowing they've been shot due to adrenaline.

Endorphins also happened to be released during orgasm. My guess is that you've "linked" sexual release and pain release, and are thus seeking the next endorphin "hit," if you will. People who try to stop cutting often encounter difficulty due to an "addiction" to the activity. The addiction isn't to cutting itself, but to that endorphin release.

Please note that I am not a doctor, thus this should be taken with a grain of salt. I would still highly recommend you seek a therapist to discuss that past abuse.

I hope I was able to be of some help.