Asking out my best friends ex?

you mean ask her out behind his back?

or just plain think about her and keep it to myself?

just plain think about her and keep it to yourself. Bc if you would do it behind his back dont be surprised when he shows up at your house at 4am with a brick

Weak dude...very weak. Dont do it. I will personally kick u in the nads. Joking. Ask her out if you feel comfortable with doing it. You know your friend better than any of us. Ask your self, "is this uncool or cool?"

well if i do anything im going to talk to him about it beforehand.

i dunno yet..

Its your friend, you decide.