We only see Mr. Carol's Husband Man a couple of times on page, and he's nice enough in person to Therese. Carol can't stand him, though. She never seems upset or regretful about the divorce. Instead she seems glad their marriage is over, although the custody of their daughter, Rindy, is a dicey issue.
The reason Carol dislikes Harge is because, as she says, "I doubt if he's capable of loving anyone, really" (11.82). But let's be honest here: is Carol capable of loving anyone? She says she is, but the way she treats Therese more like an object than a person makes us wonder. Maybe Carol and Harge were drawn to each other because neither one of them has a large capacity for love.
Whatever the reason, Harge quickly turns manipulative, deceitful, and destructive, which Carol never is. He buys a letter from Therese to Carol from Florence the maid and uses it in court to take custody of Rindy away from Carol. He also hires a nameless detective to follow her on her road trip. It's a shady move, and it shows Harge's control issues.
Carol's relationship with Therese doesn't affect her ability to be a mother in any way—Harge just uses it to hurt Carol because she doesn't want to be married to him. In this way, he uses their daughter as an object, too. And because she is just a pawn, we never get to hear what she thinks of the whole matter. Carol has no problem sacrificing her own daughter for Therese in the end, though, so maybe Rindy is better off with dad.