[Its not important is what he wants to say, because dropping the subject and leaving strikes him as a good mission plan at the moment. But... they ended up so distant because they didn't understand each other, so not answering her question probably wasn't going to help clear up this misunderstanding. Honesty would.

Besides, she offered up something about herself, he could return the favor.

Still, this was awkward for him to admit, and he turns away from her slightly. And even when he speaks, its not the usual, empty monotone; its a little quieter, softer.]

I thought... that... you didn't believe that I could do it. That I couldn't eradicate war. That I couldn't become a Gundam. That's why you wanted to take it away from me.