I am very sorry to know about this overwhelming reality you depicted in your message. As painful as it is, it seems essential for you to fully come to terms with reality, and take consistent action based on the insight and need reality is pushing you to face after 12 years in a relationship, where your main priorities and goals have not been met, to the point you have been affording everything in this relationship, where an adult, who is not disable, has been doing nothing to show any real respect, nor healthy love or caring towards you.
it is very important to differentiate healthy from unhealthy love, once many people do feel they really experience and receive love, but on the other hand reality shows through concrete facts, how mature, healthy and constructive love happens to be.
The reality you have depicted here shows a person who seems to have been severely spoiled by his mother, and then seriously enabled by you for at least 5 years, who has not shown any accountability nor real caring towards you, and who is now reacting to the possibility of you leaving, since he obviously does not want to afford any of the consequences most people in his shoes would have to face after having taking so much advantage of a loving and giving partner.
Based on your story, it''s my suggestion that if you truly want to start taking good care of yourself and life, you should take consistent action and leave, so you could work on healing and growing, and only then, after a necessary period of time, you would see, not because of nice words or tears from him, or from any isolated and temporary manipulative change, but from concrete and consistent actions in time, if this person truly respects, cares and deserves you, rather than want to keep you in order to perpetuate his responsibility free and spoiled life.
I have seen most people in his shoes playing a nice role only for a while, fooling their partners so to fuel attachment and keep everything back on the same viscous circle, and most people in your situation codependently enabling the same pattern over and over again.
This is why I invite you to seriously consider taking good care of yourself and life, and giving yourself the time to see if this person really changes or not,, and I''d not suggest anything less than 6 months to a year. I know that time is precious to you, especially after waiting 12 years for building a family , and that''s why you could not afford getting more into something that after a couple of months would get back as before, since you deserve and need healthy, respectful and fulfilling love and caring , a mature, responsible and truly reciprocal relationship, and nothing less than that.