I can understand the fact that depression can sneak up on anyone and that life can throw bad surprises at you. What I don't understand is what the marriage is to someone in their mind if the depression takes up so much of their mind. I was always taught that a marriage is supposed to help maintain the happiness of those involved. I feel the way I do because I don't have human connections, whether they be marriage or friendship, so I often see people who mention they're depressed when they're married and have trouble fathoming how the marriage is either sufficient or was the solution.
This question was inspired by thinking back to my own parents. People usually have compassion towards those who feel down, but it typically doesn't dawn on them how it feels to be in the family itself. I grew up with a dad in whom you could often see the depression, and often I'd have an existential crisis by proxy about my parents. He ended up going to the psych ward five times because some random person called the medics on him. On the inside, you tend to think "why have you never just opened up about your ideations as long as we knew you were depressed". It feels unfaithful on a dad's part to be sucked into one and left out of the other.