I’ve been in a similar situation with someone I consider my soul mate, but I recognize why I feel the way I do, and I’m assuming you feel the same.
You are insecure, afraid to lose him. You’ve made mistakes in the past (either with this relationship or another) and even if you don’t plan on doing it again, it still effects the way you might see others because you’ve done it yourself. You have low self esteem, you don’t feel you deserve him and you think that he’ll run off with another lady, even if he is perfectly content with you.
My boyfriend and I are going through this, because I’m insecure for these reasons.
I’m trying very hard to change this feeling, but I know it is hard.
Trust your boyfriend. If he hasn’t given you a reason to be jealous, then don’t be so!