You can be his link to the future, his reason to continue trying to become and stay a good person. That 3-hour phone conversation is just the kind of thing a BPD sufferer might do. And he should agree in advance to accept this. There is time together, but also both of you are individuals, with rights to time separately. You should not have to drop everything when he calls.
Nobody is perfect.
Everyone has the right to have faults and make mistakes. This includes both him and you. If he does, this problem is a manifestation of the belief that no one could possibly love him, and therefore he needs to fight for love, tooth and nail. BPD can be overcome. He is now 33, and I would think he is genuine in trying to establish a life for himself as a mature adult.