You should know that it isn't just big breasts. It is ALL breasts. The big ones are just more noticeable (having smaller ones probably makes you a little more sensitive too).

Cleavage is like visual gravity (for women too or you probably wouldn't notice the big ones he was looking at). Kind of like a car wreck where you have a hard time forcing yourself to look away. It works the same way with a Whale Tail (visible thong), and a knee high pair of CFM boots.

I've had girlfriends sized from A-H, and I enjoyed them all. Size really doesn't matter as much as a good self-image with lots of confidence.