It's tough when someone we love is closely bonded with someone we don't approve of. Whether they are a lover or just a close friend...
My gf has a friend who I got tired of hearing about, and I told my gf that, I just didn't want to hear about her anymore. This woman was in a bad marriage and trying to leave it and kept going back to her asshole husband. My gf was her only friend left, all her other friends were disgusted with her. But lo and behold, after 2-3 years of floundering, she did leave her abusive husband and got custody of their kids. I know my gf sticking patiently by her helped.
So, maybe your bf sees something in Cassie you and Peg do not? He is driven to help her. I'd just make him aware you don't need to be in the loop, it's his business and you don't want to hear about it. Hopefully he will respect that.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
me: Mags, 58, living with:
miss pixi, 37, who is dating (NRE):