Why does Kit hug John?

Kit hugs John excitedly after he reveals his feelings for Mercy.

"John! Why should you want to talk to Mercy?"
His eyes twinkled. "Why do you think I come so often?"
"But I thought--we all thought--I mean--"
"It has always been Mercy, from the very beginning. Didn't you guess that?"
"Oh John!" In a burst of incredulous joy Kit flung both arms rapturously about his neck. With a startled glance up the road, John tactfully freed himself. His very ears were pink, but his eyes were shining down at her.