I was recently asked, in PM, similar questions with regard to my relationship with my, now absent, ATF, whether or not i thought the quality of my marriage helped me keep things straight, and if a crappy marriage might easier to succumb to a deeper emotional attachment, or the illusion of one. I thought they'd make decent discussion topics. Based on the responses thus far, I think I was right. :)
My wife and I have more than sex, but she simply isn't as interested in sex as I am. The sex part with strippers fulfills that aspect, but most strippers aren't interested in anything more, so I haven't had any problem keeping things separate. I suppose if I didn't have the type of relationship that I do, it might be different; I could see mistaking the interest displayed by some girls as being more than financial.
In fact, MFC(Classic) and I had a discussion about our "relationship" once a couple of years ago. She had to come to terms with the fact that I'm not going to fall in love with her, leave my wife and support her full time just because she's a superb fellatrix. :) She did, though.