What is triangulation in relationships?
Let's say that you have two friends who are married, Sam and Cindy (names are fictional). And let's say Sam comes to you and bitches and complains about Cindy, instead of working out the problem directly with her. You listen. You're empathetic and supportive. You might even feel honored and connected now that Sam is opening up to you.
Hearing all the bad things Cindy has done, you start to feel resentment toward her. Meanwhile, Sam–who probably feels much better now, because he has gotten stuff off his chest–has unknowingly transferred his problem with Cindy onto you.
Not only is your behavior towards Cindy going to change (you'll probably act distantly or angrily towards her), you will feel emotionally exhausted, and you're most likely going to unload what you've heard with people close to you; talking about Cindy and Sam to others might get back to them creating yet more conflict. This type of complaining destroys all three relationships within the triangle.
What to do?
Avoiding the triangle
Avoiding these situations, cutting them off at the pass, and removing yourself from such conversations is really hard. In a perfect world, one should be able to say the following:
“I think it would be much better if you talked to her about how you feel, rather than to me.”
“I value my friendship with both of you. So, please don't put me in the middle."
“I can tell this is really hard for you, but I feel uncomfortable when you tell me such private details concerning your marriage.”
“I don’t feel qualified to give you advice. I think this is something you might want to bring up with a marriage counselor.”
So, you listened to HIM, you're mad, and now what?
You're only human and you have just listened to a load of crap and now you're outraged, exhausted and need to get rid of it. Sharing what you know and your feelings is not a bad thing but doing so with a friend or family member who also knows Sam and Cindy may be risky. I know... I've been there. Sigh.
Here's what's worked for me. You can take it or leave it.
To process what I am feeling and to come up with a game plan on how to go forward with my relationships, I've used journaling, writing a letter and NOT sending it, and talking to my therapist (to deal with the feelings) and to my coach (to deal with the game plan).
In situations like this, I needed objectivity and confidentiality, which both a coach and a therapist provided. Family and friends are not objective, as much as they might think they are.