Jealousy

If you love someone, why is there jealousy? There has to be trust. If there is no trust do you really have a relationship? I struggle with jealousy too but it is mainly because of my self esteem. I have come a long way in gaining more self esteem but I still have a way to go. I know that I am not young and beautiful but I also know I have some very good traits. I am not sure how to overcome the jealousy but I do not want it to ruin what I have. Trust is the key. Trust who I am and also trust my partner.