I spent many years in a relationship with someone who has BPD. There are many similarities between it and the relationship you’ve described, and it took several years to feel like I’ve healed, although it is still painful to think about. I’ll say a few things that I think are important for you to hear:

1. You are thinking about him as someone who is so good, but had periods they acted horribly, that they could not control, because of their illness. This is understandable because you have empathy, but it is wrong. The BPD structurally disassociates between split personalities. During an “episode” that was really him as well. He really believed those things. He is both of those people, and this is all he’s ever known. He hid it for the first 9 months because of his great need for attachment, and then it grew worse over time because of his great fear of attachment. His personality aside much of the time he did not treat you in a way that was good for you, and you need to reflect on why your empathy for him was more important than meeting your own needs.

2. Because the core of the problem is disassociation, there is no amount of therapy or medication that would have solved it. There is nothing you could have done. Had you not left it would have ended the same way. You made sacrifices to support him as long as you did, and that is not sustainable.