It wasn't that he didn't trust her - he did, pretty much completely. But after having just found her again, the thought of going to sleep and waking up only to find her gone again -

Like a cold cabin in Colorado, the last vestiges of fever wearing off, and she's gone, gone, he can't find her -

But he was exhausted, he had no idea how long it had been since he actually slept, and sometimes, he did just need to trust her. Let her do what she needed to do. So he nodded, though he looked somewhat hesitant.

"If you're sure you'll be all right."