to me it sounds like a genuine obsession. it's severely disturbing and disrupting to you, it doesn't have much basis -- you've never had involvement with men, and you aren't attracted to men sexually -- and you can't let it go. Constant doubt is a big OCD thing.

you probably know already that most people feel the occasional attraction to someone of the same sex, or fantasize about it, but that doesn't make them homosexual. it's just part of human sexuality. so occasionally imagining yourself kissing some guy doesn't mean much.

i've heard of other people with this, or some other kind of disturbing sex-themed obsession. I have some thoughts like that.

it does sound pretty rotten to me. are you in any treatment?