He had accepted Harris' hospitality, had eaten freely of the good things Harris had provided, and the boys would vote him a prig if he left them for his bed as soon as the feast was finished.

It would seem that he was afraid of being discovered absent from his room--as if he did not dare to share the danger with them.
Frank was generally very decided in what he did, and it was quite unusual for him to hesitate over anything.
There is an old saying that "He who hesitates is lost." In this case it proved true.
"Oh, all right, fellows," said Frank, lightly.

"I'll stop a while and watch you play." "But you must take a hand--you really must, you know," urged Harvey Dare.

"Our game is small.

We'll put on a limit to suit you--anything you say." "I do not play poker, if that is your game." "Don't you know how ?" "Well, yes, I know a little something about it, but I swore off more than a year ago." "Nobody ever swears off on anything for more than a year.