You are a wonderful person, i hope you know that. 16 years is a long time to dedicate your life and support, albeit to your loved and dearest.
Mental illness is a beast, ive seen it. Not in the same situation but ive seen it all the same. It was my parent. Its hard work and that's why they have professionals to deal with it. Sometimes 2 or 3 different specialists just for one patient... you're just one guy.
There has to be point where you think about yourself and put you first. Its what you deserve.
I feel you did all you could. You should sacrifice things in your life sometimes for the ones you love, its proof that you love them. But that doesn't mean you have to sacrifice all that you are. You need to retain a sense of self.
I hope you find happiness