Jealousy is comparison. And we have been taught to compare, we have been conditioned to compare, always compare. Somebody else has a better house, somebody else has a more beautiful body, somebody else has more money, somebody else has a more charismatic personality. Compare, go on comparing yourself with everybody else you pass by, and great jealousy will be the outcome; it is the by-product of the conditioning for comparison.
Love shouldn't be about jealousy or anything like that. It should be about commitment and being able to trust that person. If you can't have that from the get-go, there's a problem.