Hi, Baf93
I've seen you've been already posting and sharing. There are no super duper experts with magic answers on this. We all make mistakes and those mistakes are our tools to learn. You are already helping others, and that's the spirit.
I'm sorry you're going thruough this. It is awful to see the person you love (and loves you) dissapering, sometimes they're there, but they are no longer the person you knew, and you get more and more desperate to have them back. I'm really sorry about your child, I can't imagine how that must feel.
My SO can't leave for some days because she has kids, I help her raise them, but she wouldn't leave them alone with me without a plan for them to be safe and not scared. But she leaves while she is still there. She would avoid me and look at me with total hate, and then be perfectly rational and affectionate with the kids. And that makes me scared.
I hope he comes back. This time he has a couple of real big things that would make anyone feel more unstable, the engage, and the loss of a child. We wish them to solve those things with us, as a team, but many times they can't lean on us. They don't think they deserve our help.
Maybe next time he cries and tells you something is wrong, you could tell him that you understand how that would make him feel very lost and hopeless. But that knowing what is the reason of his pain, would make help more possible. Knowing that is has a name, that there are plenty of people feeling like him, and that there is treatment and ways to maki things better, can give him a little hope.
The same of knowing something is wrong with them makes them react against therapy, and labels. I find useful to talk about this as one kind of pain, not disorder. Stressing it is hot their fault, they didn't ask for them, some very bad people did this to them (his family?). And as it was the doing of others what got them here, it needs the doing of others to get out of that.
As I'm sure you've read. The "recipe" for BPD can be sumarized as a very sensitive kid whose adult figures as a kid invalidated their experience, to a point that they coundn't trust their vision of reality. The adults that were supposed to teach them concepts like truth, trust, love, loyalty, perseverance, altruism... .Showed all the wrong things instead. Sometimes it doesn't take evil people to do this, but I think I've read that in your fiance's case, it was.
I have the theory that with a little bit of nourisment (and honesty) as kids, people who would have had BPD are the trully brilliant people who make our civilization grow forward, the Einsteins and Motzarts. But it's like they have a lot of raw potential twisted in all the wrong directions.
They would seem (be) immature in a lot of decissions, because they left their childhood with a lot of pending subjects.
After he figures out what it's troubling him, he needs to make a real commitment with you, and with getting better. If you are getting married and you're already thinking about kids, he can't just turn off his role on that family. He can fail, but he has to try. That's my opinion.
Good luck and hang in there. I hope you have people to talk to, don't be alone all the time. Take care of yourself.