Most Helpful Guy
I disagree with all these people saying ''Everyone does that!''... I never knew that they personally know everyone in the world, wow! That's pretty cool.
They must read minds :O.
As long as you're not constantly thinking/fantasizing about other guys, and don't plan on acting on that fantasy it's alright.
Most Helpful Girl
Everyone fantasizes about other people. A lot of people misunderstand what monogamy is.
Monogamy is a choice to be with one person. Biologically, we are not meant to be monogamous, we're meant to procreate. Being monogamous is a social and moral choice. It doesn't eliminate our desire to want to have sex with other people, we just override it and choose to stay with one person.
Let him go, he doesn't sound worth the time if that's how he's gonna be.