It's only when she's been gone for a few days that he goes after her. After all, these days, a few hours is rarely anything to worry about and going after them is only likely to get you killed instead.
And Melanie's tough, as well as good. The Seekers won't catch her - or at least that's what he tells himself.
He almost hates it that he cares so much, because one of these days she could get captured and then it's the caring about her that hurts. Because then it's the face of the people you care about betraying you, and not just some random stranger.
But Melanie is too good to get caught and if it's close to it, he knows what she'll do (he agrees, even if he hates it).
She's not going to get caught.
It becomes his mantra.