Stephnananana
You should have a talk with him and definitely bring up how your daughter feels about the ex leaving.
What kind of schedule do you have as his time and your time? Is it one week on one week off?
I think not bringing any s/os around your daughter until it's become an established healthy relationship would be best for everyone.
He should be able to tell these women that he doesn't want his daughter to meet them until further into their relationship.
This. It is 100% possible for him to avoid bringing an SO around your child if he wants to make an effort to do so. It's one thing for him to be reckless in his own relationships, but inflicting those decisions on your child is senseless.
I would just broach the subject gently and explain that to him. He may be able to handle a breakup without problems, but he's a grown man.
I wish you the best!!