Jealousy is stupid enough but sexual Jealousy is truly falling into a hole. It means one is comparing one’s capacity to satisfy a partner sexually and feels poor in comparison with another person. All such impulses (they are not really emotions) rise from some low and dark state of being and must be seen for what they are using the discernment. If he favours another person over you because of sexual needs then it speaks much more about him than about you. It means that there was something else behind the mask of love and you should be happy that the mask is off before you decided to live with him forever. In any case sense lies in letting him go if he wishes to be with someone else. That, after all is true love. So come out of it asap. Jealousy is a very dark state and scars the soul.
Affectionately,
Alok Da