All of this rings true for me as well. I don't have a problem getting an erection when I MB, or most of the time when I was cruising stangers for sex. But in an intimate relationship, as soon as I begin to doubt my partner's feelings for me, or my insecurity gets the best of me, I may as well forget about sex. Same thing happens when I've been thinking about my CSA (triggers of any sort). I've tried the Viagra route, but even that doesn't always work.
Another thing that will cause me to lose an erection faster than you can believe is if my partner should say, "I just want to satisfy you, make you feel good." I don't know for sure, but I suspect this might have been the kind of thing one or more of my abusers might have said.
In any case, this particular aspect of my life is probably the most troubling of all my psychosis. It doesn't help my self esteem or my partner's, it clouds communications (see "How do I let the people in my life know it's not them" in the Gay Survivors' Forum) and it's frustrating as hell.
This isn't much help, I know, other than comiseration. I'll be watching this discussion though.
Lazarus (Yes, truly brought back from the dead, just not often enough... LOL)
"That which does not kill us, surely makes us stonger." - Neitsche