I know I have.
Triangles are a natural part of life. According to family therapist Murray Bowen, they will form naturally when the tension in any dyad becomes too much to sustain (1972).
Some triangles are healthy and helpful, for example when work colleagues struggling with a piece of work approach their boss for some help, or when two quarrelling siblings go to their mother to keep the peace and prevent a fight.
‘Triangulation’ becomes a problem when there is tension that can’t be resolved in the primary relationship and a third person (often a child or a parent / parent-in-law) in brought into the relationship to side with one person, forming a triangle.
This has the result of creating closeness between the person who has been brought in and the person who brought them in and more distance between the people in the primary dyad.
Take the example in the image. Dad’s are fighting and unable to resolve some core marital issues. Dad ‘A’ brings in their daughter to side with him. Over time their relationship becomes closer as dad ‘A’ showers the child with gifts for siding with him. Dad ‘B’ feels isolated from the family unit and withdraws into work as an escape.
What needs to happen here is for the couple to get some help working through their issues, so they are not tempted to involve the children. Problems in relationships are the norm, not the exception. Most people at some point need help in their primary relationship.
Reference: Bowen, Murray (1985), “On the differentiation of self (1972)”, in Bowen, Murray (ed.), Family therapy in clinical practice, Lanham, Maryland: Rowman & Littlefield Publishers, Inc., p. 478, ISBN 9780876687611.