How do I tell my fiance about this sub?

She's self conscious about the size of her breasts. I think she'd like to know about this sub, but I don't want her to think I don't like her breasts. I love her breasts. They're the perfect shape, even if they are on the small side. I tell her I love her boobs just about every time I see them and she's become more comfortable showing them off to me. But she still regularly comments about wishing they were bigger. I'm worried that if I tell her about this sub, she'll take it the wrong way and lose the progress she's made building up her confidence.