Lilliwyt, I don’t understand why you think we should care about Kaoru beyond her role as Uta’s potential love interest.
She’s depressed? So what? She’s done absolutely nothing to help herself or to deal with the obvious problems in her family situation, even though she’s had every chance to do so.
Her main strategy seems to be to just wish for the impossible—that everything was back the way it was, before she found out that her husband was (probably) cheating on her and her little sister-substitute had romantic feelings for her. That’s the emotional maturity of a toddler, not an adult.
Sure, if there’s going to be a Kaoru-Uta endgame, they have to get back together somehow, but Uta deserves far better than this pitiful excuse for a person.