What's happening when our feelings are hurt to the point where we are unable to forgive or reconcile?

Conflict is inevitable - but there's the type of conflict where people can repair the relationship, and there are times where our feelings are hurt to no return and we've written the person off permanently.

What's happening in our brains when we reach the point where we suddenly hate the person and want them to disappear forever? Is it some specific emotional reaction, like neurons that completely break the attachment to the person, that leads us to be unable to reconcile?