Victoria and Conrad Grayson, Revenge
Queen V (Madeleine Stowe) and Conrad's (Henry Czerny) deteriorating relationship on Revenge makes for riveting TV, but only because they're so horrible to each other. Their cold, loveless marriage was built on a foundation of betrayals, lies, and framing other people for terrorism, so it's no shock that their divorce is a bloodbath — and in some episodes, we mean that literally. They'll both use anyone, up to and including their own children, as pawns in their twisted game, and they'll do it with a chillingly polite smile.
Dishonorable mention: Nolan (Gabriel Mann) and Tyler (Ashton Holmes). Because hooking up with a crazed conman who later stabs you and leaves you tied to a chair is pretty much the opposite of romantic.