Yeah that is pretty fucked up. That' why I will never commit to marriage. I've also fucked around with married woman and I always think after "wow that was pretty fucked up"... I don't know if I would do that again..
Setting rules from the start (Like telling them it's only about sex) is ok but they never abide by them as time goes on and they get more emotionally involved. Married women are just as scandelous as single women. Does marriage mean anything to anybody these days? But nonetheless I would still tap it.