Jealousy can be experienced at any age. In a study published in Developmental Psychology in 2005, researchers defined jealousy as a sense of threat to a valued relationship; that relationship could involve a family member, a friend or a romantic partner. The feeling can extend to other relationships as well. For example, one friend could be jealous of another friend’s relationship with an instructor or other authority figure. According to research published in Human Communication in 2011, there are various types of jealousy: sexual, romantic and emotional.

Feeling threatened by your other relationship and afraid of losing your friendship, your friend may act in a manipulative manner. He may try to make you and another person stop liking each other. Sometimes the jealous person may act with verbal or physical aggression. Alternatively, the jealous friend may suddenly end your friendship in an attempt to reject you rather than be rejected. Judith Orloff, author of “Emotional Freedom,” claims that this kind of friend likely suffers from chronic low self-esteem and a fear of being unlovable.

Some people understand that jealousy is a normal emotion. When they feel pangs of jealousy, they stop to ask themselves why. Karla McLaren, author of “The Language of Emotions,” suggests that people use the feeling of jealousy as a sign that the relationship needs attention. A friend with a healthy level of self-esteem will do just that and will probably approach you to talk about your relationship with the goal of making it better.

If your friend has acted badly, recognize that she is feeling hurt and insecure. Gently broach the subject of your friendship and ask if there is something you can both do to strengthen it. You may be able to talk things out, understand what led your friend to feel jealous and repair your relationship. At the same time, be clear about behaviors that are not acceptable to you; if your friend behaves with verbal or physical agression, it may be better for you to end the friendship.