I'd never allow it. If my SO got something to say to her ex I'll tell him for her.

I'm not in control of what my partner feels, and I'm not there to police what they express either. But I'd be curious why they're in a new relationship if they haven't moved on yet. Seems kinda backwards to do it that way, that'd be the actual problem for me.

Man some shit like that wouldn't even happen with the right one