Small A cup...boyfriend says he doesn't care?

I wear a 32A however my boobs sometimes don't fully fill in a 32A depending on the brand. My boyfriend is a butt guy and says he doesn't care at all that I have a very small chest. He's a guy, I know he likes boobs, but not nearly as much as butt. Even though he really makes me feel like he doesn't care that I'm a 32A, I still feel somewhat un-womanly. We shower together all the time and I still find that I cover my boobs with my hair a lot and oftentimes keep a bra or shirt on during sex. We've been dating for over a year and I am 21. How can I feel confident with my itty bitty titties and stop comparing myself to other girls? How can I get more comfortable letting my boyfriend see my boobs? (He has seen them in their entirety but a lot of times it's only for a moment)