Come hang out with us on the parent with BPD section

There are two posters who recently posted about their MIL with BPD.
Understandable that you feel invalidated, but it's also possible your H doesn't know how to be validating. He, himself may have been invalidated by his parents- and you possibly were too. It is something we can learn to do better and there are tools on this board to do so.
My BPD mother was very sensitive to feeling invalidated. Interesting, even though her extended family members don't have BPD- they tend to be invalidating. I don't think they mean to be. I think it's a skill that wasn't role modeled in her family. Sometimes, family dynamics are passed to the next generation. Perhaps their parents didn't know how either.
That's with non disordered family members. When a parent has BPD - there's more to the experience than feeling invalidated. What is interesting is that the family dynamics where there is a parent with BPD are similar to those where a parent(s) has alcoholism. It's said we match our partners in some ways in terms of dynamics (even if it isn't the same disorder) and so, you and your H have matching experiences in some ways.
Also, while your H doesn't have BPD, and I don't either, and you don't have alcoholism, we may have learned behaviors that helped us during our childhoods in our family of origin but are not serving us well now. It's good you are in counseling. I hope your H is willing to do this too. Individual and possibly marital.
Your in laws are in their own dynamics. One possibility is that FIL is the emotional caretaker, rescuer, for your BPD MIL. On the Karpman triangle, your MIL has victim perspective. FIL is rescuer/enabler. This was the dynamic between my parents.
My father at one point got ill- and what you see is that FIL has an illness- and an illness that requires care. What happened with my parents was a change in the dynamics. While it's logical to see what is happening, with BPD- her reality was based on her feelings, and her feelings is that she's the one he's supposed to be meeting her needs, not the other way around. She saw this as him taking away his attention and caretaking. He wasn't doing this on purpose. He couldn't do it, but she didn't understand that on an emotional level. Without his emotional caretaking, her BPD behaviors escalated.
This may be going on with your H's parents too.