“If the person you bring in is not a professional then it is not a helpful way to resolve conflict,” Counselling Directory member Kimberly Tomlinson tells Stylist. “Arguments, even the loud, mean or nasty ones, are private, sometimes vulnerable discussions that should stay between the members of the relationship.”

When you rope in someone else, you break the zone of trust and open communication. Suddenly your partner has a new person to consider, and may not feel able to speak freely (especially if that person already seems to be on your ‘side’). They’re also likely to feel more than a little resentful towards you for ‘ganging up’ on them, notes relationship expert and psychotherapist Neil Wilkie.

“Triangulation is unhealthy and unhelpful,” Wilkie says. “The third party is likely to take sides that favour the person in the couple that they know better. The underlying problems are likely to be about feelings; a third person will keep the argument stuck at the level of who is right and who is wrong. It creates dependency and avoids the couple learning how to argue well.”

Plus, that third person will bring their own baggage into the situation, which could make a minor argument spiral. “As much as the third person wants to help, they will have their own biases and narratives which could hurt the couple’s relationship,” says Vasia Toxavidi, British Association for Counselling and Psychotherapy (BACP) therapist and member of The Couples Collective.

Think about it – say you’re having an argument about phubbing, and you bring in a pal who happens to have discovered their partner was cheating on them after they were always on their phone. That friend is going to have a whole load of bias and may escalate the issue to new heights. You weren’t even talking about infidelity… then your triangle brought that to the fore.

Triangulation is the red flag habit that’s wrecking your relationship’s trust