I've found that my jealousy, though much lower than seems normal, still varies considerably. 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. Of course, that doesn't mean that variable explains all jealousy variation in the population. As for testosterone: anecdotally I haven't noticed anything when my testosterone level increased following a change in diet and exercise.