Lessons
Nobody knew why Thorin began spending so much more time with Ori that autumn, but twice a week they would get together for what they would only call "lessons".
When Bilbo asked what they were doing, Thorin would simply smile; and all Ori would say was that Thorin had sworn him to secrecy.
So, while everybody wondered, nobody knew - and Bilbo grew more and more curious and worried about the secret that was being kept from him.
That is, until the first winter snowfall, when Thorin gave to him the gift of a heavy cloak that he had knitted himself.