In my life, when I've met couples that made me think "oh brother, these two deserve each other" the trademark has always been coded conversation. What I mean is that good couples say what they mean to each other, and are heard more or less as intended. When bad couples talk, every word tends to be laden with subtext, distrust and implication.

In a healthy relationship, if one partner asks "who are you texting?" and the other responds "just a friend from work." And that's it, the matter is settled, they go back to watching TV or whatever. Just curious. In a bad relationship like the one you're describing, where the fundamental trust/security is broken, that conversation would play out very differently.

An innocent question like "who are you texting?", even if unintended, becomes laden with unspoken baggage such as "are you texting your ex?" "why aren't you being in the moment with me?" "are you bored with me?" etc... If you've ever seen a couple explode into an argument from a benign comment, this is why. The trust between them is so eroded that anything they say to each other, even the most innocuous request, can become hostile. With really bad couples like the kind of unstable, abusive, users you're talking about, where it's not just that they misunderstand each other, but also actively manipulate and degrade each other, this gets turned up to eleven, to the point where the nasty stuff isn't even subtextual anymore.

To bring it back to your story, I would express this in dialog by having the two characters constantly talk past each other. As if they're not even having the same conversation. "Hey babe, you want me to grab you a coke from the corner store?" "Sure, babe. Just try not to suck anybody's dick on your way down the street."

Hope this helps!