It's the same as the case 3 on that link.
''My husband takes me for granted. He pays me as much attention as he does the wallpaper.''
''Meu marido me desvaloriza/ Meu marido não me dá nenhum valor..''
''I am sad because I feel he takes me for granted, ...''
''Eu estou triste porque ele não me dá nenhum valor/ porque ele não me dá nenhuma importância/ porque ele me desvaloriza/ porque ele me dá como certa na vida dele/ porque ele conta com o fato de que estarei sempre aqui não importa como/...''
As I said, you can say this in one million different ways. This sort of term ''take for granted'' is kinda it would be better understood from what comes next, it's like it needed a complement and it's not different in portuguese. In your example, ''...he just assumes I will be forever next to him without him trying to work on the relationship.''
There is no exact and accurate term to define ''take someone/something for granted''. I could tell you one hundred more. It depends on how emphatic you want to be and even on your personality, for example.
I'd stick to ''desvalorizar algo ou alguém''. Most likely every person here would translate your example in a different way. I'd translate it into portuguese like that:
''Estou triste porque ele me desvaloriza e acredita que eu estarei sempre aqui por ele incondicionalmente, mas não é bem assim''
Feel free to ask anything you want to!