I normally don't post in this forum but your thread caught my eye (yes something I deal with as well...except my H and I still have sex together)
I may have missed this as I skimmed through the several responses but here was my initial thought:
He knows he does not satisfy you sexually, you are not attracted to him...he can be whatever he wants to be online...sexy and attractive with no worries about really satisfying his "partner" They tell him what he wants to hear and vice versa...he can be a sex god and they may have multiple orgasms...definitely an ego boost for a man who doesn't satisfy his w (or his exw).
When I found my H was doing this he told me it fulfilled a sexual and intimacy need I wasn't (me being the LD partner again is different from your sitch).
Just a thought, would you want to have sex with someone who told you you didn't satisfy them??