None of the signs are sequential, which I think is an important note. They are simply 6 characteristics couples have during arguments that, if present, give a very good indication that that couple will not stay together.
Sign #5: Failed Repair Attempts
A repair attempt is one partner's efforts to deescalate the conflict between them. It's putting the breaks on the argument so that flooding is prevented. The repair attempt doesn't have to be eloquent or articulate. It might be one word, or a look, a gesture, a touch.
For example, a husband might hold his hands out and say, "I'm sorry. I shouldn't have made that comment about you mother." The wife then would need to respond to this repair attempt, maybe offer an apology of her own or verbally recognize her husband's apology. A girl might reach over and cover her boyfriend's hand on the steering wheel in an effort to end the silent treatment they have been giving each other since a fight over dinner. The boyfriend might give a smile in response, indicating he's willing to break down the wall between them.
What Gottman found in couples heading for divorce was that one partner didn't respond to the repair attempt or another or that repair attempts were never made. Usually it's the partner who is flooded and disengaged from the argument who rejects or doesn't even realize their partner has issued a repair attempt.
The presence of this sign between couples in your novel is an almost guarantee that they won't stay together. Accuracy of prediction reaches into the 90th percentile when partners don't respond to repair attempts made. The four horsemen can run rampant in a marriage, but if repair attempts succeed, the marriage is probably stable and happy.
Sign #6: Bad Memories
The last sign Gottman discovered that was present in couples headed for divorce court is an inability to recall their past life with anything other than negativity. Gottman calls this "rewriting the past" when the current negativity in a relationship distorts the past, which at one time likely had been positive or the couple wouldn't have gotten together.
When a couple remembers the low points and none of the high points, it's definitely a sign. In fact, Gottman said, "When I ask them about their early courtship, their wedding, their first year together, I can predict their chances of divorce, even if I'm not privy to their current feelings."
Next week we'll conclude this series by looking at the argumentative tendencies of men and women.