Tom had lost himself.
He thought marriage would bind his thoughts to her only. That it would be her and him and a whole empty world.
These feelings were still here, and they wouldn't go away. Tom couldn't hide himself away, either-he had to keep himself busy.
Tom pretended everything was normal. Becky and him were together, and Huck was back, and they all went to school and did their homework and hung out, and they were all happy. Tom was happy, the best he could be.
...Which was not at all.