Vindictive Addiction

There's a game people play... Namely couples, where it seems to be a competition on a standard of who can hurt who the most, and doing it so well, getting away with it.

This "game" is essentially triggered by an inevitable difference. It tends to more often than not be easy to settle, until one or the other notices an opportunity to exploit the prior bout, to "get back" at the other and even attempt to do it worse.

It's like a game of tag. Initially, it's supposed to end when the flag is thrown in or the two decide to grow up and move on. But in most cases, this game can be found appealing to one party and the game just keeps escalating.
Meanwhile, the victim reciprocates the vindiction. But no sooner than after, the two find themselves stuck: ping-ponging the effort to win the game of who hurts who worst.

Strangely, neither party is aware of this and find themselves continuing until there's nothing left of the (what would've been a) relationship to exploit.