Trying to influence a person through people you both know
If you still have things that are left unsaid, you might want to clarify the situation and try to change the opinion of your mutual friends. It seems that if you talk to your ex’s mother or best friend, they might make them return to you. But this won’t work.
Why it’s harmful: The person will most likely feel like you are pressing them. Especially if the close people try to do the same and talk them into starting the relationship again. The pressure will make them more convinced that they should stay away from you. But it’s likely that nobody will even try to talk them into this, so you will just waste your time telling other people about your problems.