I don't understand how you can justify wanting to lie to him through omission - were you in his situation, wouldn't you want to know? Or would you really prefer that everyone lie to your face in order to keep you happy?

Assuming he would never find out is almost childishly naive, Mustang; the fact of the matter is it's his life, and everyone here knew the outcome but the man himself. The fact that you don't acknowledge how hideous that is, choosing instead to hide behind childish hopes and ideals based on how things should be, is a perfect example of why I say you've learned nothing.