Hi and welcome to the site though I am sorry for the circumstances that brought you here. You are in a good place to learn and get support for your situation.
My son has come very close to an emotional breaking point himself and needs a level of ‘intrusive’ support to be able to maintain any level of stability in his family.
Can you describe what you mean by 'intrusive' support? Having a supportive family member is very important for people in relationships with pwBPD.
We have many members who are involved romantically with a pwBPD (person with BPD) whether diagnosed or undiagnosed (uBPD) and some have made improvements in their marriages. Certainly we offer many tools that can help you understand some of the behaviors and how best to respond. For example:
BPD Behaviors: Extinction burst and intermittent reinforcement?Extinction Burst - The term extinction burst describes the phenomena of behavior temporarily getting worse, not better, when the reinforcement stops.
Spontaneous Recovery - Behavior affected by extinction is apt to recur in the future when the trigger is presented again. This is known as spontaneous recovery or the transient increase in behavior. Be aware of this eventuality. It is a part of the extinction process. Don't be discouraged.Don't JADEJADE stands for justify, argue, defend explain, or rather don't do those things when in an argument with a pwBPD. Doing those things can make it worse and often the pwBPD will feel invalidated. on top of that you end up feeling resentful.
Understanding the behaviors and learning better ways to communicate can help a great deal. As you continue to post, we can make more specific recommendations for your situation. I think the biggest thing to work on is boundaries. How are you with establishing boundaries with your DIL? We can help you with that too. Boundaries can be tricky but are vital to learn.
How old are your grandkids? Have you shared your suspicions about your DILs diagnosis with him?
Please post so we can help and let us know how things go tomorrow. We also have two other boards that you may find helpful to read. One is a relationship board titled Bettering a Relationship and the people who post there are all focused on using the tools we promote here and helping and supporting each other. The other board is the Son/Daughter and Son In-law/Daughter In-law board. The parents working on improving and coping their relationship with their kids are also very supportive and encouraging.
Anyway, I am glad you found us and decided to post! Welcome!