If it was after you left, ummm how do you know they made out?

you'll find someone who's going to be worth your time, you shouldn't be anyone's option.

Everyone is someones option at some point. Most people play the field these days until you sit them down and have the "exclusivity talk" which if he just asked you out might be a little early for that talk. Go on the date and see what he's like.

Unless it was his girlfriend, which I doubt, that means nothing! I'd still give him a chance to redeem himself. :)

I guess you should kiss him goodbye then!

This is silly. He just asked you out why would you have any pretense of exclusivity? Sure, not everyone has the capacity to court more than one person at a time(I don't), but at this stage you must realize it's a possibility?

Drop him. Preferably on his head.

He asked you on a single date and that means he is off the market until you decide you don't want him? That's not how dating works. He didn't ask you to marry him, right? Just go on a date? There was no agreement he'd place himself on a shelf to await your leisure? I guess I don't get the idea that you're locked into a monogamous relationship with someone you haven't even gone out with that first time yet. It takes time, and more than 0 dates, to come to this MUTUAL agreement to be exclusive.

Hack his Facebook page and change his status to in a relationship. Start a catfight with the other woman. Make a giant scene. He needs to understand that once he asks you out he belongs to only you forever.

After- are you spying on him- if it was before or after your time.... It really isn't your concern...and sounds like your to jealous, you just met him..... Did you brand his ass, a sign of ownership ?????