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.
It is cowardice to hide your gambling habit from your spouse, you can decide not to tell another person but your spouse is your companion till death or divorce. People should be open about their likes and dislikes before marriage, it is good to discuss everything so that nothing will come as a surprise to their partner. It'll be deceitful to learn that your husband or wife has always been a gambler if they told you otherwise before marriage. The spouse at the receiving end will find it hard to believe anything said by the lying partner afterwards. Better to let everything out before joining in marriage so your partner can accept you for who you are or move on.