I love my wife but I'm just compelled to put my willie in strange ladies after handing them money' territory, it's a different kettle of fish. That's when I put an appropriately sympathetic look on my face and allow the words to drift over me like a gentle breeze
I have the same problem and this is the way I see it: Basically someone signed a contract with another person (in the case of marriage it would be: I'm taking care of your needs in exchange of you not sleeping with other people). But then somewhere along the lines one of the parties decides to make some "benefits" on the side (without the other parties consent of course) and "breaches the contract" ( he just wanted a piece of the cake and to eat it too! hey what's wrong with thaaaaat?). Then he feels all guilty and wants you to feel sympathetic for him.
Sure I'll put the "you poor uncomprehended little thing" look on my face, but only because you're paying me ...
(I guess that makes me another candidate for "Evil, embittered prossie of the year ward' lol... )
the thing is i think that part of the monogamy contract, whether explicit or implied, is the assumption that sex will be happening within the relationship.
i don't particularly like the monogamy model, but nonetheless i can see that the deal cuts both ways. we will be sexually exlusive, and we will try to meet each others sexual needs. he never agreed to be celibate.
if i was in a monogamous relationship and my beloved partner stopped having sex with me, whether by choice or because they no longer could, i might well look elsewhere for some no-strings sex. as my client said, as long as he does not have a relationship with someone else, ie an affair, and all that he is doing is having his sexual needs met, then he doesn't truly feel this is being unfaithful. perhaps its rubbish and i am just being naive, but i think the reason i accept this is because its pretty much what i would do too.
ps i dont believe anyone so far has said anything evil at all! just pragmatic.