Why do teens cheat in relationships psychologist research?

You don't need a psychologist or a study to answer that question. People of all ages cheat in relationships because they are not being honest with themselves, and/or they never think about the real reason that they're in the relationship.

First of all, if specific commitments to an exclusive relationship have not been made, seeing other people while in a relationship with someone does not constitute cheating. Assumptions made by either person in the relationship don't count.

You will find people in relationships for many reasons other than they like this person and this person is someone who is appropriate for their personality, and the other person feels the same. A relationship does take a little time to develop, but sooner or later, the appropriateness or inappropriateness of the relationship will show itself. Far too many people won't admit to the inappropriateness and walk away.

You will find people in relationships that only exist in their own mind. They believe or assume that the relationship means exactly the same to the other person as it does to them. The other person may even say things that support their belief, but relationships can't be based on Words only. Many people are fooled by the Words when the actions don't match because they are maintaining their own fantasy.

These two are just the tip of the iceberg of reasons why a person is cheated on, which makes it easy for the cheater. A cheater is not only being dishonest with their partner, they're usually just as dishonest with themselves. You will hear so many different excuses for their behavior but the bottom line is that cheating is a way to avoid a reality that they don't want to deal with or an exercise of power over another person (the person that they're cheating on), usually a combination. In both cases the cheater's lies to themselves will be reflected in the excuses that they may give, but they're just excuses.

Teens are no exception and even more vulnerable to the images of 'relationships' rather than the reality. Teens are inexperienced and subjected to the beliefs of their peers (just as inexperienced as themselves) and bombarded on all sides with images from the media. Teens are easily deceived by messages from music, movies, TV, and magazines; messages that use teens vulnerability to sell them images and things.