My bestfriend asked me out to make someone jealous?

I think you should say no. You should not be a rebound and deep down ask yourself if you are a girl that's "worth it". If you are worth it for any guy, tell your friend no, he needs to stop using you cuz you know what? if the other girl gets jealous and wants him back, he's going to leave you for her...so avoid all the drama and simply say no.