I think your breast size is wonderful. Both men and women spend way too much time worrying about the size of their breasts or the length of his cock. The sexiest woman I can remember had very small breasts and beautiful perky nipples. She was so sensual and could get me more aroused and satisfied with sex than anyone I knew. I didn't have a large cock and was a little shy about her seeing it the first time but she was able to do remarkable things with it.
So, don't worry and be very proud of your body. If it matters to him, then he isn't worth your time anyway. And, for heaven's sake don't go down and get a breast implant. They don't feel very good to the guys anyway.
Medium, but if he truly loves you. He isn't gonna care what they look like, just don't care what size boobs the girl I want to date has , that is because to me and many other men find all boob sizes are all equally sexy, because boobs are boobs. I want to date a girl for her personality , not her body. I want to date a girl that has the following: big heart, mature, kind, polite, and has an amazing personality. All that matters is in the inside not the outside (this can apply to both genders).