The realization of bpd can be very overwhelming.
it can be.
and you should go into this relationship with eyes wide open, as far as "what it takes", and understand that it may never be an "equal" relationship.
that said, few (if any) of us enter into our relationships with the skills and knowledge needed, and we often make things worse. there can be a lot of room for improvement.
the short version is that if you are talking about committing to marriage, its pretty important that independent values and interdependent values are (still) compatible. you will need to determine if his relationships with other women are something you are prepared to accept and live with, or a deal breaker; dont bet the farm on it changing, it may not.
was he recently diagnosed? what led up to the diagnosis?