He'd never considered, not from the first day, that she'd say anything other than yes when he asked this. It was the only possible thing she could say and have the world be right. If she didn't, he wasn't sure his mind could have survived it - so it had never been considered, even when he knew she'd likely have been safer with soemone else.
"We're tied together, you and I. I won't pretend I understand what magic it is, because it certainly isn't something we've worked ourselves, but as desperate as it may sound, we're a part of each other."