Thorin knew that they were in a new territory when it came to their relationship, but he too felt that he needed to be honest with his feelings. Somehow keeping them from Bilbo or lying about them just seemed wrong to him. So, he was determined to make sure he was a open as he could be, even if it was a bit awkward for him.
The kiss to Thorin's cheek did surprise him, so for a moment he didn't say or do anything, but once he had processed what happened it didn't take him long to decide how he wanted to respond. He leaned down and placed a tender kiss to Bilbo's right jawline, allowing it to linger. He thought that said everything that he wanted to say in the moment. So, he leaned back on the couch, his arm still wrapped around Bilbo, and he smiled at the Hobbit.