I guess that it's a natural feeling. Even if people love each other, they can't avoid jealousy. 

I mean jealosy between two people (wife and husband, a couple).

I agree with Aisuly. it's a natural feeling. but I'm not a jealous person.

Between wife & husband. Maybe. If they have, they must overcome this. otherwise this will effect their relation.

Jealosy for relationship. 

If a person is jealous to another one he or she loves, could means he/she can not get the same in return.

If you love your boyfriend, sure also hope the return will come from your boyfriend as the same that is called jealous as the same as some one else has. 

Or you just hope so many people whom you don't like to love you that is not jealosy. ha~~