#1 Well, sorry for my English first, my Spanish is a little poor to make myself understood.
People feel jealous in love because they care, as a girl myself, if my boyfriend feel jealous, I think it is OK, because if he feel OK when I'm with other guys happily, then I'll feel that he doesn't love me, or at least, not so love me. Think about it, if a man love a woman, how can he bear that she has a lot of fun with other guys. So, jealous is common psychologically. U needn't worry so much about it.
However, too much jealousy will ruin love. u cannot ask your girlfriend/boyfriend to be always with u, no more contact with other boys/girls. That will make she/he think she/he should belong to u, freedom has been lost. Even, they will feel u r selfish. The end will be a tragedy.
Then confidence and trust are importanrt.
Here is a saying: If u love a bird, then set her free, when she still comes back, it is yours.
So, to be jealous is OK, that means u love her. But u need to deal with jealousy, if she is ur destiny, then she will be there.