"Please, clouds, don't rain!" Not going to work, is it?
And neither will trying to reassure someone who just can't be reassured. They will go on fretting, no matter how you plead.
Chronic insecurity in your relationship is a major problem. Why? Because relationships really, deeply matter. Your health, your wellbeing, your happiness are affected by your relationships more than any other factor. And your most intimate relationships have the biggest effect of all.
Admit it or not, relationships with others are important to us as human beings. Relationships with parents, siblings, friends, boyfriends, girlfriends, professors, roommates, and classmates can bring joy and takes on added significance in our lives. We learn that it is often in or through intimate relationships that our romantic, companionship, and intimacy needs will be met.