Assumptions
He'd always assumed they would have time to really explore their feelings for each other once the war would be over. It only once had crossed his mind that maybe they'd never see the end of it. But when they survived the first major attack he didn't worry about it anymore. Now he realizes how foolish he'd been.
Standing next to his friends, safely back on Earth he can't help but wishing himself back to a time where he still had her standing next to him. Or at least to a time where he still had the hope to find her alive and bring her back. He wishes himself back so he could do things differently, to have the chance to voice his feelings out loud and not only let his actions and looks speak of them.
It's his curse for the rest of his life. Living on, regretting and dreaming of a life with her that could have been and never will be.