<human>: Give me the gist of the text in a nutshell

My parents have been married for 20 years. Won't go too into depth about my father's affair, but long story short he was planning to just leave us hanging next year and run away with his mistress. (Which, okay, whatever, good riddance.)

My father's a narcissistic piece of trash who thinks that responsibility towards the family is just paying the bills. He's not important, I don't really care what happens to him from here on out.

Anyway, my mother has sacrificed a lot for our family. She gave up her very promising career to care for us because my father was a workaholic who never came home. (She had to give up her job to care for my brother, who has a developmental delay. He still requires care, though not quite as much.) With all that has happened, my mum feels like she's lost her dignity. She no longer has a career, she's been humiliated and insulted, and my father is just waiting for the divorce papers to be served so that he can leave with no responsibilities.
<bot>: Mum feels shitty because she gave up her entire life for my father and it didn't pay off, how can I help her get through this?