Triangulation can take many forms:
Third party reinforcements
Recruiting allies as a form of bullying. The goal is to force their partner into accepting their viewpoint through the use of persuasion, embarrassment, majority rules or guilt.
In healthy relationship, partners do not use third party messengers to settle differences or arguments. Should they be unable to solve the issue themselves, they will turn to professional/qualified help, such as a therapist or a counsellor who will be unbiased.
This triangulation technique consist of pitting two people against each other. This is usually used by the toxic partner as a ploy to separate their partner from friends and family without them realising it. They feels an intense euphoria when they turn people against each other, especially when it’s over a competition for them.
They will do this by smearing the character of one or both of the people behind their backs. It is manipulative, hypocrite and a red flag abuse technique.
Replace, then dump
The final triangulation happens when they make the decision to abandon their partner. In other words, this triangulation technique is used by the emotionally abusive partner when deciding to end the relationship. Instead of breaking up and being direct about it. They will keep the relationship going while secretly looking for a new partner. Once they have successfully found someone, they will dumb the old partner by telling them they’ve fallen in love with someone else and take enjoyment in the additional hurt it creates.