My male friend who is 28 is dating a 32yo woman. He bends over backwards for her and pretty much obeys her every word but now myself and a few other friends of his are getting concerned as to how she's treating him. I've known him for a while and we don't really speak much unless I'm passing on a message from my boyfriend to him (my boyfriend doesn't have social media) or if I'm asking for advice, this is because his girlfriend forced him to block me on everything. She's messaged me on numerous occasions behind his back calling me a slag, saying he wants nothing to do with me (which he's never said), and just downright being disgusting towards me which she has apparently done to majority of girls he knows of, even if he doesn't talk to them. She's broken up with him dozens of times for no reason then goes down to his house without permission banging on the door begging for him back and (unfortunately) he always takes her back. When she breaks up with him she'll post screenshots of guys she's talking to or tinder chats and says "I'm going to go on a shagging spree to forget you. I'm gonna fuck someone else and I won't be thinking of you trust me".

I know it's not my relationship so not my business but I care about the well-being of my friend and just needed someone else's opinion on how she's treating him. This isn't healthy, right?