Fibrocystic & insecure

so a few months ago I went to the doctor because I had found a lump in my breast, and she told me it was nothing to worry about I was just fibrocystic. so the lump shrinks and grows but i’ve noticed i’m more insecure about it recently. I just got into a new relationship and the other night we were being intimate and he grabbed my breasts and I immediately clenched up. it was like I was just waiting for him to cringe and pull back or something.. how can i get over this?