I have read through these posts since I related to your concerns in.neverland. As a matter of fact, it is the whole reason I joined these chat rooms because I couldn't stand it nagging at me day in and day out.
I don't know if you would put it this way but I almost see it as feeling guilt about my own sexuality. It just feels wrong and dirty, some people would say I was seeing it as a "sin" but I am not religious and believe sex is a natural and important part of our lives. But I can't shake that feeling when I masturbate, let alone the idea of sharing myself sexually with another. It stops me dead in my tracks!
I saw it as an issue of just getting comfortable seeing myself in a sexual way, meaning I have been pushing out of my "comfort zone" and that has actually pushed me to seek some third party because I want to work on this but can't be objective because if I had it my way I would recoil back into my old ways. So I started going to chatrooms and "having sex" seeing it as a baby step towards the real thing, but it is causing me a lot of anxiety so I am not sure yet if it is helping or just wrong move.
I am sorry if my ranting doesn't give you any concrete answers, but at the very least know, you are not the only one.