My boyfriend always says I have small breasts.

If your boyfriend is only joking with you on the occasion of two people, it will be considered as a joke. If there is a third party, it will hurt your self-esteem. You should explain your feelings to him. I think he will attract attention. In the future, pay attention to his words and deeds. What he said should be just a joke, but if you don't pay attention to the occasion, the result will be different.