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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 depends pretty much on the point of view of one's partner whether gambling is a dirty secret and a reason to distrust one. Mostly, because there are people who have a life which was built from the ground up with religion and also due to traumas in their family history having something to do with gambling, alcohol or something else.
For example, if I had a girlfriend who experienced neglect and lack of resources when she was a child because her father was a addicted to gambling, then I would not be surprised she would be willing to break up with me because I am a casual gambler.
Though, regardless of what each person believes about gambling it is always good to be open with one's partner and tell them from the very beginning one has such a hobby or activity to kill time. It is better than trying to hide something for literal years until found out, destroying a relationship.