any more information to give? examples, instances, etc...
in general a good thing to do is make a boundary and stick to it. like warn your partner that you respect their feelings and want them to feel comfortable within reason, but if they let their jealousy go past a critical point again, then you will walk away or hang up or stop talking to them, or some other action. i.e. set a consequence for him or her not owning the jealousy and dealing with it well. then stick to your part of the plan.
more details would elicit a better response, however. So what is going on in particular?