I had to edit your question down to just one question according to enotes regulations. Please remember you are only allowed to ask one question alone in each group per day.
Concerning the banker in this excellent short story, there is plenty of evidence to suggest that he regrets the rash bet that he made so long ago with the lawyer. Certainly, his financial situation has definitely made a massive difference to his thinking, as if we loses the bet, he will be made bankrupt. However, perhaps the best quote to focus on is when he looks back at how the bet was made and concludes:
"It was all nonsensical and meaningless. On my part it was the caprice of a pampered man, and on his part simple greed for money..."
This clearly shows the banker's regret at his hasty bet. In addition, consider how the banker responds having read the letter left by the lawyer:
When the banker had read this, he laid the page on the table, kissed the strange man on the head, and went out of the lodge, weeping. At no other time, even when he had lost heavily on the Stock Exchange, had he felt so great a contempt for himself.
It is clear, therefore, that the banker now looks back with an immense sense of contrition and fear about the bet, until the point when he reads that the lawyer intends to renege on the terms of the bet and thus loose the money, where he still feels an intense sadness.