Just letting you know, that might shock him a bit and he'd need time to mull it over. Be prepared, as painful as it could be, to end the relationship if he doesnt like that idea and try not to be to hurt, its unfortunate but his attractions are important and it would not be his fault if he wants to move on
Hopefully he's a good guy and at best will accept you are male regardless of need for surgeries etc., and at worst he'll respect you enough not to say anything offensive and quit on good terms. I suggest educating him on the idea of transmen first before telling him that you are one so he can get an idea, grasp, or understanding beforehand
