One challenge in coParenting is the introduction of a new partner. The emotional landscape when step-parents are involved is complex.
The parent forming a new attachment has expectations for an intimate relationship with a new partner. A coParent/former partner may still have feelings about the loss of the old relationship. Unresolved feelings of intimacy may result in attempts to limit the role of the new partner, even competing with the new partner.
It may seem right to insist on dealing only with the other parent on the basis that the new partner has no parenting role. But think about it. That person will be spending time with your child when you are not around. Do not create resentment of the child that makes your child’s situation in the other parent’s household less tolerable.
It is easy to slip into a competitive mode with the new partner of the other parent. The competition is commonly phrased in terms of who has the right to parent and who is butting in. No one wins when the relationship with the new partner is adversarial. A new partner may also be testing the loyalty of the child’s parent. If you butt into the newly formed relationship, it will not be well received. Your child is caught in the middle with no way to retreat.
It is best to back away and let the new relationship resolve itself without your involvement. After all, you have no control over how the other parent and new partner interact. If you try to impose your standards or insist on limitations to their roles, you are creating conflict without any power to resolve it. Unless there is a serious issue that fundamentally affects the welfare of the child, you are better off staying away from competition or confrontations with the other parent’s new partner.
A healthy alliance can develop when the adults focus attention on meeting the needs of the child rather than fighting with each other.