Split on my bestie 😢

So... I've tried to make this post once already but I went over the character limit because I don't know how to make anything brief, so this is attempt #2

The other day I was having an otherwise AMAZING conversation with my best friend of 13 YEARS over the phone when she casually let it slip that she's considering moving back across the country because her boyfriend doesn't like it here. SHE is perfectly happy here, and they literally OWN their home, but HE wants to go back across the country because he doesn't want to be here for some reason?? He doesn't like anyone in his family and REFUSES to even fly back home to visit for special occasions, despite the fact that she has been BEGGING him to go see his family, so it's not like he has anyone he's trying to go back for.

My best friend is a complete pushover and has had a LONG history of getting into abusive and controlling relationships, and this one is no different. I've witnessed a pattern of manipulative and outright abusive behaviors from this particular boyfriend in the past, and this feels like just another attempt to control her. He has proven time and time again that she is not his priority, and he only seems to care about himself and his own desires. He even recently tried to guilt trip her into risking her own life driving in a snowstorm that was so much of a risk that the local authorities made it ILLEGAL to drive unless it was an absolute necessity... All because he was "bored and lonely" (and wanted her vape because all of his were burnt to a crisp)

I've tried to warn her that he's not good for her but she will not listen to anything I have to say on the subject, and EVERY TIME she gets into an abusive relationship, her partner ends up not liking me and tries to distance her from me. She usually agrees to this and cuts contact with me because she's more afraid of losing a romantic partner than me. I've lost her more times than I can keep count of at this point, and didn't hear from her AT ALL for SIX YEARS the first time she moved across the country... So the thought of her doing it again scares the shit out of me.

I truly don't know what to do anymore. I love this woman more than I've ever loved anyone in my life. I would kill for her and I have already risked my life for her once. Ending the friendship is not an option in my mind, but apparently neither is her ending her relationship.

What do I do???