I think her husband's neglect of her for 2 years is a an acceptable reason to cheat, so I won't blame her for when it happens. Still holding my judgement on ML since we don't know his situation yet, but if it's similar to hers, then I'll probably accept it too.
I think divorcing would be better, though I don't know how Japanese society treats divorcing so maybe there are repercussions I don't know about.