Did you think that just because Cam is heroic, virtuous, and brave, that he was going to live happily ever after? Not so much, Shmoopsters. Which isn't to say he gets an unhappy ending—instead, it's more like an in-limbo one. In the end, Cam writes to Pin:
"I am tall and grown now […] and I stay away because I no longer know how to come home. When I figure it out, then expect me! You could not do better than Acton Mansto. Of course I think of you all, all the time." (16.144)
Cam admits he doesn't know how to come home, and we're betting he doesn't mean he can't figure out the route on a map—instead he's still figuring out how to get on with his life when so many other people died in the war. Dealing with all the guilt and nasty looks from everyone takes a toll on the guy, and by ending the book in this sort of unfinished fashion, we're shown that he's still dealing with the repercussions of the war. He's working his way to a happy ending we think, but he just hasn't quite gotten there yet.