And it correlates, as far as I can tell, with general self-confidence. If I'm feeling down about myself I feel much more possessive and attached to significant others. When I'm feeling good about myself I've been fine with open relationships.

This has been my experience too -- jealousy almost always comes from a place of insecurity. For a while my standard jealousy first-aid was just to make an extra trip to the gym/practice some other skill I could feel good about improving at.