I want to kiss my friends ex
why do you want to kiss your friends ex?
She looked strikingly beautiful and I can't control myself
You should learn how to control yourself. It'd cause pain to your friend if you kissed his ex. You should prioritize your friend in this situation.
I'm not sure. We are close.
If you're close, it's even more reason to not disrespect your friend. You should discuss your attraction to his ex before taking any action.