I have never cheated in a relationship, and never will. Yes, I look at other women, lust after them, even fantasize sometimes, but that's as far as it goes, because I could never break the trust and promises made in the relationship I am in.
In my life, very few women, less than a handful, have ever come onto to me or flirted with me (that I know of!). Am I hideous? No. Am I a gorgeous hunk that ladies swoon over? No. Am I clueless as to signals given off by women? Maybe, who knows. I do not actively pursue anyone when I am already in a relationship, or trying to build a relationship.