Well, as a guy all I can say is that sex isn't that high up on my list of pleasures and I would never risk a relationship for it.
You can say what you want about me on the other thread about being tossed off in public and that means I have loose morals, but I have never, ever, cheated on someone before and I never will. Cheating is for weak people with no sense of duty, and people who have no sense of duty are scum.
A lot of men I know don't even respect women, merely just use them for sex. I often get called old-fashioned or prude because I have old fashioned views regarding relationships/sex ... this is exactly why, I don't like where our society is heading. I don't even know how I feel about raising a daughter here, will she too be used for sex!?
You're showing a real amount of naivety if your opinion on the entire male population is determined by one guy. Your sister should improve her standards, that's assuming she's still with him.