My MiL loves to talk about BM and the life she had with DH (which according to both DH and BM was miserable). She even does this when it’s just me and her (which happens rarely because BM has no boundaries when it comes to anything). 

I find it really rude, but know if I said anything it would all become about me.

I see a counselor due to BM’s harassment and attempts to control our home. The counselor told me “maybe it’s good for you to only see your in-laws one or two times a year” after I told her about how both MIL and BIL try to meddle on BM’s behalf.

Yep! All the time! My MIL does love her son...but she has a weird obsession with BM who is CRAZY.

What I think?? DH's dad left MIL way back when DH was pretty young......I think MIL is still bitter about it today...over 40 years later. So when DH left crazy BM after a pretty long marriage....MIL sided with BM for a long time and even somewhat now even though she tries to hide it. I think MIL is siding with BM b/c of how MIL felt when her hubs left her years ago......like father like son? haha MIL will do NOTHING to piss off BM but no care for DH and I and how we feel about anything.

My MIL would have preferred her son to stay married (and miserable) to BM for the rest of his life.....just to keep BM happy. She pretty much said that when he approached her about divorce........