Coming from someone who is the one in my relationship who despises my boobs, I can tell you that it's difficult.
I'd imagine it's different for everyone, but in my experience, I want to let my boyfriend enjoy my body the way he used to before I was truly in tune with my own gender. Breasts, for most, are an area that can bring pleasure and comfort, and I can't imagine how hard it must be for him to have to turn a blind eye to them for my sake. It really makes the whole "Us time" thing a little strained.
But as someone said in an earlier post, it helps to take that emphasis you would want to place on the breasts, and instead direct them at the neck or back. Anywhere with pleasure receptors really, that are not gender specific.
Also, something that helps with me, is that above my boobs, I have an entirely flat area and for me, it resembles the flat chest I long to have, my boyfriend caught on to this, and will concentrate on that part of me, as it is pleasurable for both of us.
I feel like this is something he might want to bring up to me actually, but might not to spare my feelings.
I really hope all works out well, and just so you know, if you two really have a great relationship, a conflict of how to ignore his chest will not hinder you for long. It just takes time and communication.