TL;DR what is TRP's plans on how to breakup with a crazy GF who may harm herself or my Bro due to the dire situation

Alright I don't trust R/relationships advice or any other subreddit i could have gotten this question answered for obvious reasons known to the the majority of this community but my bro need a solution and Trp seemed liked the logical place to go. My bro who is 19 and his GF who is also 19 have been together for over a year now. She is about a 5 or 6 on a REALLY good day which is perplexing to me since he has been able to pull solid 8's and 9's in the past but i digress. When they first started dating i despised their relationship and thought it doomed to fail from the beginning any mere mention of this was brought with hostility so I shut my mouth like a good friend and expected him to realize that fact soon enough.. no dice. Fast forward an annoyingly long year later they are still together and she is living with him barf now why do i have so much disdain for his GF? lets start. She is extremely bi- polar , not very smart, completely dependent on him, has virtually no other friends, always tags along on our 'bro nights", complains endlessly , she actually almost broke up a friendship between Him and another guy in our circle, never stops talking, and has successfully created an atmosphere that is unpleasant to be around. Our entire friend circle had been in agreement so we formulated an 'intervention' to snap him out of it and he agreed with complaint we had. So whats the issue? He claims he has no idea on how to get out of the relationship. He's tried before but then she starts crying and hamsters her way back into the relationship. Now my friend is beta in the way that he has this weakness of being nice to a fault with is SO so just straight up cheating on her is out of the question for him. we thought of a plan to try to get her to cheat on him since that's an easy way out but there is no way she would risk her sense of security on cheating on him. The scary part is she is a little crazy and he wholeheartedly believes that if he breaks up with her the wrong way she may try to either harm herself or him. They also had a apartment together for 6 months so he is afraid that she can legally take his stuff do to Texas law. anyone can see how toxic the relationship is but i believe she actually thinks everything is fine!! If anyone on reddit can help formulate any type of plan or variation of the suggestions we gave him above it would be TRP.