I'm going to ask my friend to not go to a concert with my ex
Do you really plan on asking him?
When you hang out with my ex it will make sense. You do not want to do that.
It's not okay to tell your friends what to do. Even if it's uncomfortable your friend can hang out with whoever he wants. Maybe you can discuss with him how it makes you feel instead of asking him not to.
Dude, I just hate when my ex is happy.
It makes sense to have some resentment towards someone you used to be in a relationship with. It is just not realistic to think you can tell you friend who they can, and who they cannot hang out with.