I find it's very important to be secure in yourself. Often jealousy issues can stem from a fear of not being good enough and being abandoned. The common thought process goes something like this: "If we see other people, he might find someone better than me and leave me." This line of thinking is caused by a lack of confidence. If you're confident, many of those fears about being left for someone "better" go away because you know that you have value and cannot simply be replaced. And, if you recognize that each person is unique and valuable, you can better understand how your partner's other partner(s) enrich their lives.