Hello crystal23 and a warm

Any breakup/makeup in a relationship is painful, and having that cycle repeated, in addition to being painful to you as an individual, can negatively impact the relationship, too. That is challenging to have multiple instances of that cycle in your >2 decade marriage... so sorry you are going through that.
When you say that the events are 10 years apart, do you mean that his stepping away happens ~10 years apart for no visible reason, or that there have been catalyzing events that happened to be 10 years apart, that he reacted to? Let me know if that doesn't make sense -- trying to figure out if, for example, high-stress things have happened that influenced his stepping away.
Borderline personality disorder isn't really diagnosed based on breakup/makeup cycles alone, though unstable relationships characterized by idealization/devaluation, and also damaging impulsivity, are two areas that might be looked at. Typically, for an official diagnosis of BPD, a person must have at least
5 of 9 features.
That being said, in a sense, the issue isn't really the
label of what's going on... it's your H's
behaviors (regardless of label or diagnosis), and the impact of those behaviors on you and the relationship.
We can help with that -- being in a relationship with a pwBPD (person with BPD) often takes some non-intuitive tools and skills, especially in the area of
communication.
...
Can you describe these "stepping away" times some more? What does he say? How do you typically respond?
Do you want to stay in the relationship?