[Kamui can be oblivious, but he's not stupid. Subaru's comment, and all of its implications, are glaringly obvious to him. He freezes, but then looks way. It should be obvious to Subaru right away that something is wrong. Kamui's not smiling, and he doesn't look happy.]
[In almost any other situation he would have jumped at the opportunity, throwing himself into the relationship with glee and committing himself wholly to it. But the situation he's in right now... accepting wouldn't be fair to Subaru, and he's not naive enough to pretend otherwise.]