I’m Dating a Person Who is Frequently Jealous of Me. What Can We do About it?
Sometimes jealousy is intentionally provoked and the cause is obvious. Jealousy, however, can also occur in situations where there seems to be little basis for it. Where there is a frequent and strong manifestation of the emotion of jealousy, the real cause is usually the inadequacy and insecurity of the person with those feelings.
Some jealous people have excellent qualities — gentleness, sensitivity, graciousness, for example — and yet they are very insecure because of the problems from their background. If you yourself are secure and are willing to make a commitment to help such a person, through patience and open communication you can possibly help rebuild that person’s sense of security and thereby reduce his or her jealousy.
Taken from The Teenage Q&A Book, pg. 154