Instead of looking at jealousy as the problem, let's look at our reactions to jealous feelings as the beast for us to tame. Our feelings are what they are. They may not always be based on facts, but they are real. Our feelings don't hurt anyone, as long as we don't act impulsively or irrationally on them. So here is where we can intervene. We can check ourselves when we are feeling jealous by asking what are the facts and what is our imagination. Many times our jealousy is connected to the imaginary thoughts we think our partner has (ie. he thinks she's sexier than me) or the imaginary fun we assume our partner is having without us (ie. she late because she's out having drinks with other guys). Our imagination then makes the situation appear and feel worse than it really is. This imagination we have then impacts our relationship when believe it to be true and it leads us to be suspicious or accusatory of our partner. And of course, you can imagine how it can snow ball into something bigger as a result.
We can also check our jealousy by asking what personal insecurity the jealousy is triggering in us. Many times our jealous reactions have more to do with our feelings of inadequacy (ie. I'm not good enough, I'm not sexy enough, or it's only a matter of time before someone leaves me) rather than the reality of the situation. When our feelings of inadequacy are triggered, we tend to inflate other people's qualities and this makes us feel inferior. It's very difficult to be objective and rational when we are feeling inadequate, and often times we go into defense mode. We seek to protect our self esteem by blaming our partner (ie. you are always doing things behind my back or you're the reason I can't trust you) or by trying to control our partner. Unfortunately, jealousy often does not end very well when it gets to this point.
Love is always stronger than jealousy, yet jealousy can so easily consume a relationship. Given that there's no evidence of infidelity in the relationship, it's important to remember that jealousy only grows when we feed into it.