I'm going to ask my dad to stop talking to my ex husband or cut him out of my life
Why do you want them to stop talking?
Yes, my dad is becoming too friendly with him and it's awkward
Maybe they just get along very well. You should not try to dictate who your parents can and cannot talk to anymore.
But my ex was terrible to me.
You should talk to your father, then. Tell him you concerns, not try to dictate who he can talk to.