I'm posting here to stop myself interfering where it wouldn't be helpful. Just need a rant really.
My closest friend (let's call her BFF) in the world got CP'd last year to a lovely woman (DW). They're both beautiful, bright, passionate, creative, funny, lovely etc etc and perfect for each other in lots of ways, but also both quite neurotic. Both children of alcoholics - the DW suffers from depression and sometimes struggles with her own drinking. Meanwhile BFF is clingy and afraid of being abandoned (childhood issues).
BFF came over for dinner a couple of days ago, in floods of tears because DW has been behaving incredibly erratically recently - going away on business, then calling/skyping at unsociable ideas saying she's freaking out and wants to die. Or whatever. Meanwhile the DW is also having an emotional affair with some other woman.
Bit of background here - BFF has been out for years, but the DW thought she was straight when they met. The DW then proposed quite soon after, and hasn't really spent much time thinking about her sexuality as a single person. I think that's playing into all this messing around.
This EA came to a head when BFF put her foot down and said 'this has to stop, no more calls/texts to this woman, no more speaking to her, no more FB, no emails, nothing.' DW went along with this, but can't seem to stop telling BFF how difficult this is for her, how upset the OW is, and tons more besides, which I think is beyond unacceptable - why the f* should BFF have to listen to how much the OW is suffering??????? 
I'm furious for BFF. I know she can be clingy and has most likely been enabling the erratic/freakout behaviour by always being the one who soothes/calms DW down. But the DW's behaviour is completely unacceptable.
But I don't really see what good it can do if I get involved. And yet they're both really good friends of mine. And it breaks my heart to see BFF so upset. And it breaks my heart to see them going through this. And I'm furious with the DW and really struggling to sit on my hands and not get involved.