My STBX wants control of MY child's life when he's with me

I’m in the early stages but there is already a wrinkle. I have a plutonic (but opposite sex) friend who has grown to love my 11yo son over the years and now that I’m separating she’s helping my son deal with the changes (she’s a teacher). My son’s mom [STBX] is saying that he can never see this friend and certain family members - not only while he’s visiting me, but FOREVER. She’s angry at my friend because she knew I was leaving months beforehand but didn’t tell her. Can she do this? Can my soon-to-be ex exercise that much control over our behavior even while not in attendance?
And isn’t this a bad idea for my STBX in regards to her future relationship with her own son? I mean, when he finds out he’ll react and I’ll guess not well.

Comments? Suggestions? Can she do this?

Unless your friend is somehow a danger to your child I cannot see that a judge would order you to prevent your child from seeing this person.

Unless the “friend” is a detriment to your child’s well being, your ex has absolutely no say so who is in your child’s life when the child is with you. An ex cannot control who you see or who your friends are. Once divorced, you are a single person with children. Use your own good judgment about who you bring into your child’s life. But, your ex has no say so. The ex probably isn’t going to like anyone, but that is just too bad. But, use good sense and good judgment. It’s a different world once divorced and the children are the first priority. Make careful selections. That’s just the way it is. But, you are free. Just don’t abuse the freedom. Set a good example. It’s tough, but you have to show them how to do it right.