I don't think that just because Betty never worked for anything, or because Don was abused, he's suddenly absolved of all wrongdoing for his pathological abuse. I also don't think that Betty (or anyone, for that matter) should forgive Don based solely on his background, because he's a pretty unforgivable misogynist. Yes, the pattern needs to be broken, but when you consider the inescapable damage he did to Betty's mental health, it's not fair to suggest that she forgive her unapologetic abuser.
I agree! A Night to Remember frustrates me so much because Betty is frantically looking for proof that Don is having an affair, but she doesn’t find anything. She goes INSANE trying to find something! And in the previous episode, the thought of Don fucking another woman makes her physically ill. It’s so heartbreaking.