There are 2 issues at play here:
1) Thanks to the way the Japanese language and social normities work, people will very rarely SAY what they mean (it's usually treated as something vulgar), and even when they do it can be misconstrued based on context.
2) When you've dealt with serious psychological abuse it often becomes difficult to find your own worth, and it makes you feel like you're a burden on the people who care about you. (Trust me, I've been dealing with this for a loooong time).
Right now he's in a spot where even though he understands that her feeling for him are strong, he doesn't see himself as WORTH those feelings, so the idea of her wanting to date him makes no sense in to him. It makes LOGICAL sense for for them to get together, but he's fighting instinct and that's not easy.
My suggestion: Just ask her out. If you don't know if it will work out or not, that's literally what dating's for.
