I need help

So me and my bf have been together for a while now, and he makes sexual jokes about how big his dick is. It turns me on but im also flat chested i wear a 32b and i feel that i look disgusting. It makes me nervous when he says these things becuz what if we do go down on each other and than see how small my chest is..... is there a way for me to be more confident for when that moment comes??