If you gamble it is of your interest and that of your spouse, you both need to share same orientation about gambling or given a chance to understand and respect the other person gambling choice and if they won’t then either they go or you reconsider your choice. Why should an adult keep their gambling choice away from their lover that’s deceit to me. Gambling is not a dirty secret.
I understand the grounds for break up even though I think it may be too harsh. However since I wasn't there it, I can not judge how the guy responded to the accusation. Maybe he was being defensive. If that was the case then I side with the lady. Anyways the lesson is clear be opened in a relationship. If they are going to accept you, they will accept all of you and if it is going to work out it would. If they are not going to accept you, they don't even if you were a saint.