When do you know it?s right to call it quits on a relationship?

I?m 27 F married to 27 M. we?ve been married a little over five years, getting married when I was almost 22. We dated a year and a half before then.
He?s a good man. He tries hard. I just feel like I?m suffocating under the pressure of disappointing him. He?s told me he hasn?t been attracted to me, physically or emotionally, in years. That he can?t depend on me and feels like he?s pulling all of the weight in our marriage. But I feel like I am barely holding us together and if I stopped trying everything would fall apart, and he wouldn?t even notice. I came into this marriage a confident and competent woman, but I feel like a shell of myself. I know I?m not perfect, but I really am giving it my all. I just know that my all still isn?t enough to him, and that?s demoralizing.
I don?t want to quit. I don?t want to give up on us. But I feel like if I stay I?m going to end up succumbing to the depression?. Please help. How do i know I?ve tried enough?
TLDR, I feel like a shell of a human, but I don?t know if that?s enough to end a relationship. I don?t know if I?ve tried hard enough


Source.

For me, it was always when I came home from work and found a
DEAR JOHN letter