Hi there and

25 years is a significant length of relationship, especially given the challenging behaviors the whole time. I'm so sorry it's escalated recently, that cannot have been what you wanted for the two of you.
Did he get diagnosed near the start of your marriage, or more recently? How did he respond to the diagnosis? And do the two of you have any children?
He can recognize the symptoms after a rage, but not during and seems to have no capability of controlling it.
What does it look like for him to "recognize" the symptoms afterwards -- is he remorseful, or is it more detached than that? I.e., the difference between "you're right, I was doing XYZ" and "you're right, I was doing XYZ, and I'm so sorry that I did that again".
I have never been great at handling his "splitting". what is the best way to get through it.?
Working together in a business you own with a BPD spouse is highwire act stuff. Can I ask, in general, is your work tangible items/products, or more idea-based/intangible? Does anyone else work with you two?
Does he recognize that he sabotaged your work, when he is regulated again after raging?
I have never been great at handling his "splitting". what is the best way to get through it.?
How would you approach his splitting in the past?
A good starting point here is our
workshop on splitting -- when you have a chance, you can check it out and see what seems relevant to your situation.
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Fill us in some more on your story, whenever works for you;
kells76