Hi Missingmykids and a warm welcome to the group
Really glad you reached out for more support; I hear the pain and loss coming through loud and clear in your post.
How long has your son been married? And how old are your grandchildren? It's so difficult when kids are put in the middle of these adult conflicts, I get it.
When you would try to apologize, and when you were informed that you were XYZ, were those times in person? Over email? Phone call? Other?
And are you currently in a relationship right now? If so, how is that going? Is your partner/spouse supportive of you in the middle of this?
You're definitely not alone in being a grandparent when there's a SIL/DIL with BPD type traits and behaviors in the mix. Settle in, check out the other threads, and we're looking forward to hearing more about your situation, whenever works for you.
-kells76