because they can. because they are not in love any more. because they never were in love but got married anyways. because they are bored, and for some people variety is the spice of life. because men are away from home on business a lot. because some women are easy, because all women beleive much of what we hear, that's how i have been in relationships that started with a guy lying. oh, yes, men are great liars. there are probably other reasons i can't think of right now.