No relationship is an island unto itself:  There are in laws, children, friends, political parties, neighbors and pets, all of whom can serve up a poisonous stew of triangulation unless a couple is trained to look out for this vile brew.
Typical triangulations are: a child and one parent talk negatively about the other parent (sometimes in front of them): one parent continually intervenes in the other parent’s relationship with their child, preventing direct communication between that child and parent (often the parent “thinks” that they are protecting the child); an in law or friend drives a wedge between you and your partner by seducing you to “take their side”, or asking you to make choices “for your own good”, that are not shared with or discussed with your partner: a sibling can do the same. All may seem well meaning. But all are asking you, indirectly, to put their needs before the needs of your relationship with your partner.
A red flag should go up: Any time you are pulled away from directly communicating with your partner because someone else seems to deserve or demand priority, this is the red flag of danger.  A regular diet of this behavior is injurious to the health of the Coupledom.
The best medicine: Sit down with your partner and lay out the dilemma. This can take courage but will get easier with practice. Ask your partner to help you problem solve. Then approach the party as a couple whose loyalty is to each other first at all times.
Faulty connection in the Coupledom: Partners who feel unheard, or lack the confidence to talk directly to each other about concerns, needs and feelings, turn to indirect methods of communication. This may indicate a faulty connection in the Coupledom. If this behavior is entrenched, couples therapy can provide the tools to extinguish the behavior, often handed down through the generations, and replace it with a direct, honest and more trusting form of couples’ communication. The health of any relationship rests on trust. Indirect communications, manipulations and confused loyalties undermine that trust.

Jill Edelman, M.S.W., L.C.S.W. 2012