Background: When I started going out with DH (about 10 years ago), I met his sister, my future SIL, a few weeks later and her boyfriend (BIL), a few weeks after that, so I've known them both a similar amount of time and I've always got on really well with both of them, although we didn't see them very often. They always seemed very loved up but then started having problems, separated and are now getting divorced. They both described it publicly as 'growing apart' (FB), they wanted to stay friends etc. and while I know BIL had various MH problems and dyspraxia, and SIL had reached her limit with what she could cope with in terms of him doing things without considering her feelings, I thought they might genuinely have an amicable divorce and DH and I hoped we could stay friends with EXBIL (and saw him separately in the summer).
When they were separated SIL got a new boyfriend (who seems nice and makes her happy) and they are currently staying with us. I think SIL has been bottling up some anger towards EXBIL and wants to talk about the things that have made her angry, and I'm trying to support her as a friend and listen to what she wants to talk about (so I don't want to sit there and remind her of the good things about her ex or play devil's advocate (maybe he did that because...) when she wants a chance to be angry).
What made me uncomfortable were a few conversations, mainly between SIL and new boyfriend, when we were all there last night:
a) New boyfriend making earnest statements about how much he loves SIL and how well he treats her compared to EXBIL and generally how rubbish EXBIL is.
b) Conversation assuming EXBIL is being vindictive about splitting things that mean something to SIL, which doesn't sound like him and doesn't consider that the same things might be meaningful to him too
c) Conversation complaining about EXBIL wanting to get more than is fair out of the divorce (which seems a bit hypocritical as SIL and new boyfriend are living together but not publicly because it might affect the settlement)
It feels like it's going to be really difficult to stay friends with both of them (and SIL knows me and DH want to stay friends with EXBIL), and I already feel like I have to keep things from EXBIL which I'm not happy about. I think because I can see things from his point of view/feel sympathy for someone dealing with MH problems and because he's my friend I want to defend him, but I also want to be a good friend to SIL who wants to vent right now.
AlBU to feel uncomfortable with some of these conversations and pissed off about what feels like redefining EXBIL as if we always this awful person (particularly from the new boyfriend who doesn't know him)? And any advice for staying friends with two people who are divorcing, particularly when you're more closely tied to one of them?