This is actually more common than people realize. Teenagers can be quite influenced by matters between the parents for various reasons. In some situations, a teenager may side with a parent on moral grounds. For instance, the teen may be aware of an infidelity, causing the teen to side with the affected parent.
In other situations, a teenager may see the distress of the separated parent and may feel a need to be present as a support for that parent.
In other instances, a teen may not have felt particularly well cared for, or emotionally close to either parent, and thus may be swayed more by what a parent offers in terms of resources or material goods.
It is also important to note that what appears as a preference for a parent, may actually be a preference to be close to their own friends or school.
Many parents also concern themselves that all these mattes that may influence a teen preference to live with a certain parent, may have been subtly or not so subtlety manipulated towards this outcome.
Combined, determining what creates a teen’s preference or taking sides, can be multi-faceted. What we do know is that those teens (children) who are able to have a reasonable relationship with both parents, tend to do better themselves in their intimate relationships come adulthood.
To that end, parents are advised to keep their issues separate from their teens (good boundaries); resist using teens as confidants; do not curry favor with enticements; facilitate relationships with both parents.
If any of this appears to be an issue, then both parents are advised to seek counselling together to sort out what is going on, what is at stake, and how they can handle matters without the teenager being drawn into taking sides. Sending the teen to counselling may only embed them further into the parental issues. It’s better for the parents to try and sort those issues out first.
Given their age, while decisions still remain with parents, enforcing those decisions can be increasingly difficult. Because of that, courts are reluctant to impose residential decisions on teens. Negotiated outcomes tend to serve best.