I don't see MLC in her husband, but, who knows.
Still, only the person who took its own life is responsible for it. I understand that things/people can drive us to suicide - my maternal grandfather suffered from mental illness and took his life and my paternal aunt also suffered from mental illness and tried to take her life.
But, regardless of anything else, it were them who did it. My grandfather never seek help, a man of his time hardly would. My paternal aunt had a psychiatrist that only seemed to do more damage.
I also had a maternal great-aunt, grandmother's younger sister, who was schizophrenic. Mental illness runs in both sides of my family.
Depression does cause a lot of problems/is responsible for lots of things. Like MLC. Or suicide. Does a non-depressed person takes its own life? I really don't know, but I would say no.
Sure, MLC will make matters worst. But you are here.
Sometimes good things fall apart so better things can fall together. (Marilyn Monroe)