Hi Scarletstar,
Welcome and hello
You must be exhausted with a teething baby on top of everything else. I remember those days, tired right down to my eyelashes
It's great that your H has been diagnosed, accepts it, and is in treatment. At the same time, it can still be really tough to experience these emotional roller coasters.
Loved ones are often triggers -- intimacy tends to stir up feelings. Your husband probably is quick to trigger and slow to return to baseline. Once his moods have triggered, he probably experiences cognitive distortions in which he is the victim. Unfortunately, we cannot cure their BPD. Fortunately, we can prevent things from getting worse.
When your H perceives you are emotionally distant (for whatever reason, could be fatigue, headache, preoccupation with baby), he will think it's about him. When he asks you if you are angry at him, it's best to not JADE (justify, argue, defend, explain). That only invalidates how he feels, and how he feels at that moment is real to him. Invalidating tends to escalate the dysregulation.
You can learn valuable skills like validation, which is accepting how he feels (different than agreeing with what he says).
For example, if he says you are angry at him, validating him might involve saying, "I can see why you feel that way -- my face is neutral and I am quiet, which is how people can look when they are angry. It must feel awful to think I am angry at you, I would feel the same way."
Or
":)id I do something to make you feel I am angry? Tell me more so I can understand better what I am doing."
Something like that.
Be kind and gentle and patient with yourself while you learn the skills, they are not intuitive, I have found, and must be learned.
LnL