Well put 622.
If you feel secure in a relationship, you don't feel jealousy (or maybe just an occasional light jealousy, like if a woman hits on your husband blatantly in a party).
With my ex-husband I was not jealous at all. We even lived in different cities because of work for 9 months and I never doubted what he did.
In this present relationship, I think my jealousy is caused by:
1) He never calls me sweet names (like Sweetie or honey) and NEVER says he loves me. Not even when I tell him that.
2) He keeps lots of secrets from me. He talks to his best friends and family always from work so I won't hear. He also never tells anything about his family or daughter from previous relationship.
3) He doesn't get any personal mail at home. His computer is all locked up and his briefcase is ALWAYS locked up (and he always takes it with him when he leaves the house).
See? Jealousy is caused by feelings of insecurity. And I feel insecure in this relationship.