Hello, I am Rafael. Thanks for asking your question - I'm here to support you. (Information posted here is not private or confidential but public).
I am very sorry to know about yoru sad and frustrating situation.
I cannot imagine how frustrating and tough it may have been for you to try to cope and change this reality for the past 10 years in your marriage.
NPD like many other personality disorders are chronic mental illnesses, thus when there is no cure for these disorders, rehabilitation is possible, but would only happen if the person is truly willing to acknowledge the disorder-s, takes full responsibility for his choices, feelings and actions, and commits to work on his rehabilitation process with professional support.
As a psychotherapist I relate to you and know how frustrating it could be to cope with challenges like this around loved ones, specially somebody so close to you, and because it is that tough, we also know that we cannot provide necessary psychotherapeutic support to a spouse, that it is essential for another professional to play such role, while we focus on using our knowledge and expertise on promoting changes, working with spouse and his psychotherapist-professional to comply with his treatment plan.
You seem to have tried so hard so many things yourself and I wonder what has he done all these years in order to make changes and make of his rehabilitation process something real? This is very important, since as I just said, no matter how hard you could try, if he does not take full responsibility and an active role in his own rehabilitation process, it would never work, and time would only worsen what is already there.
I am sorry to know that all of your efforts have not include open and direct dialogue about the core issues undermining his personal and your marital life. There is no way to even consider taking the first step into rehabilitation without first acknowledging reality, that requires full honesty and openness about it. Facing reality and addressing these serious issues with empathy, compassion, gentleness and a proactive approach is the way to go. Obviously because of the very nature of the disorder, this would be tough and even overwhelming for him because of the NPD, but there is no other way to work on it, otherwise it would fall into a codependent dynamic where denial, avoidance and justification shape everything and core issues get deepen and stronger. Please be sure that avoiding external psychotherapeutic treatment would never help but perpetuate this situation, you are not in a position to be his therapist, it would not work. He needs both, consistent individual and marriage therapy, but marriage counseling would be useless without him working on his personal issues first, which would require collateral session, where you would need to participate to make it work, not as a professional but as his wife.
You have been married for almost 20 years and from day one these serious mental health illness has been there undermining your marriage, and now you find yourself overwhelmed and very frustrated because of facing the fact that it has not significantly improved, and for that to happen you need to approach it very differently, specially because of the deficiencies and distortions NPD presents.
The distortions, from lack of empathy and caring about other people's feelings - your needs and expectations as his wife- to being abusive in order to impose his unrealistic expectation and rules, to protect his core insecurities and fears, make of this situation tough, and there is no way to hope for rehabilitation, for any significant improvement unless both come to terms with the fact that he requires professional psychological treatment, and that you are there to support him, but also need to take good care of yourself.