I'm going to make out with this dude's ex in front of him
Why do you want to do that, are you trying to make him jealous?
Yes. I'm going to make him jealous so he's going to regret leaving me
I understand your anger with your ex, but you should not try to get back at him by making out with his ex. Not only is it rude, but also won't likely get you anywhere. You should talk to him instead if you have issues that you need to resolve.
You don't know him or me so don't tell me what to do. It's time to break this guy's heart into a million pieces.
It can be hard to end a relationship and it is okay to still be upset but you won't be able to move on if you are still concentrating on his life. It would be good to forget about him and move on and be happy with somebody else.