Hello @Firekittensorry this is long.... . My exh no doubt has NPD and could well have other issues. I certainly believe now he has undiagnosed ASD as our child has recently been diagnosed and I can see the similarities so much but my child has empathy...ex does not because I think he has NPD as well.
Ex was emotionally, mentally, financially and sexually abusive.... although it revealed itself gradually.
The thing that strikes me about your posts is that you are making sense of him by projecting yourself into it...which, to be fair, we probably all do to an extent. For example, you'd at you feel safer because he doesn't take your stuff to heart and you feel because he's having therapy for his pds and so are you , there is understanding.
But this understanding is coming from you. Try and look (and this is hard) really objectively. He does not have a thick skin or reciprocate your understanding, he is detached. NPD see people as useful. It's about what they get out of it. You are the one trying to please.
When you say he doesn't hurt people in front of you anymore, it is not because he is thinking about how you feel. He just doesn't want to deal with your judgement or any upset. He won't stop being like this, he'll just suppress it around you because it is better for him.
This recent argument is very revealing. He's saying he is not going to change. It is up to you to put up with his shit because you have before. That's exactly what narcs do. They find people who will look after them and try and understand them and rationalise their behaviour and forgive it. BUT even not judging him at all, he is saying that he will not make any adjustments and 'negotiate'. Healthy relationships are all about communication and trying to understand each others needs. He may have a point that his needs are his needs. That statement is really vital. He's not going to change so can you just lose yourself entirely to what his needs are? If the answer is yes, then you need to keep the therapy going and explore it. It should never be yes.
Acceptance is one thing but this isn't that.
Look up codependency. Really important.
All of the understanding and good bits of the relationship here are coming from you! You are showing him the love and care you have not perhaps felt for yourself having a personality disorder.
I often tried to remind myself at the end of my relationship that it wasn't about if I loved him, it was if he loved me. He did not. He wasn't capable.
It is concerning that he doesn't want people to know what he is so you feel that means you can't talk to your friends about your relationship. You also have distance with your family, which sounds like for good reasons for your own boundaries and his attitude may seem supportive but be careful. It'll be about his needs not yours. Do not isolate yourself for him. Your needs are valid too.
Sorry this is long. I'm sorry it's hard going through this but your reflection is good. Your ability to love and care is good. Just spend it on yourself if you can and not someone who will just take. The good things you are seeing with your man are from you, I promise.