I'm 21, soon to be 22, and have been sexually active for about two years. I've noticed since the first time, though, that I panic just prior to intercourse. I enjoy foreplay and everything up to sex, but when it comes time to put a condom on, I often lose my erection.

I have a feeling this problem is due to an experience I had nearly eight years ago. I was thirteen, and my half-sister, who was five at the time, would play with my penis while I pretended to sleep. I hated myself for it, but I was such a horny kid, I couldn't resist. The last time it happened resulted in my first orgasm. The experience traumatized me, I think, because I associate every subsequent sexual encounter with a dirty mistake. I used to despise myself for masturbating, and when my girlfriend and I decided to have sex, I think the regretful feeling resurfaced, and I lost interest.

I'm just now coming to grips with the problem, and I don't want to constantly battle with myself for the rest of my sexually active life. Is therapy the best solution? I have a sympathetic girlfriend now who wants to help me resolve this (I don't lose the erection every time...) but I haven't told her the full story, and actually only two very close friends know.

I'm tired of being afraid of sex, and I need to forgive myself and move on. Your help would be greatly appreciated.