I'm going to sleep with my ex immediately after breaking up with someone
I hope you are just joking. Why would you want to do that?
I want to fuck with him and show him my strength for leaving him.
You shouldn't use someone like that right after ending a relationship. You especially shouldn't do it with another ex.
Being used like that feels good.
That is going to really play with your emotions and hurt you more than you think. You shouldn't sleep with your ex for those reasons. It could cause more damage than you are willing to admit.