My married sister is in a 7 month relationship with a married man. She says they are only friends but says she has feelings for him. I have tried to talk her in to ending this without any luck. I guess she is in the fog I have read about.

Something that is not making sense to me is that this other man has told her he will not have sex with her until "after marriage". My sister has also told me he has had testicular cancer and is sterile (I'm glad this jerk cannot reproduce). Other than being gay or unable to get it up why would a man not want to have sex? Is my sister's relationship one-sided?

Any comments or advice?