I'm so sorry to hear about what your boyfriend said. And what you keep to yourself is yours and is private; you don't have to tell him about what's going on with your body if you don't want to. As to what he said about your chest, hold your head high. For starters, if all he's concerned with is your physical appearance, then you should remind him that you are much more than just a body, and that physicality is just one aspect of a healthy and happy relationship. Here are some ideas that might help:
1. Try making an affirmation list. This can be a list of your positive physical attributes, but should also be stuff that makes you original and the great person I'm sure you are. Examples might be "I play the piano well", or "I'm a loyal friend". Really take the time to figure out at least 10 things you like about yourself. If you need help with this, you might talk to your favorite teacher or one of your parents.
2. Keep in mind that not everyone physically develops at the same rate. Some of us are "late bloomers". I know women who didn't start their periods till they were 17! Everything tends to even us all out in the end, so be patient.
3. Many women are insecure about breast size. They measure themselves against their friends, teammates, even women they just see on the street. Want to know a secret? As a guy, I honestly don't care about how big a woman's breasts are - I care about how smart she is, how good a sense of humor she has, and whether she's generally a good human being. Sure, physical attraction is important to me and I appreciate all parts of a woman's body, but something like breast size doesn't make any difference in choosing a woman to be in a relationship with. I'll bet you'll find that most guys would agree with me.
Ultimately, if you find that your boyfriend is too fixated on the physical and isn't paying attention to who you are inside, you should talk with him about it. Read your affirmation list first, so you go into the conversation knowing your own worth!
Good luck. I hope this helps.