Unless you're a gambler yourself, you will surely forgive him/her because you know that in gambling, sh*t happens, and you can lose your money in an instant.
Sometimes sign of addiction is not noticeable including the addict himself if he is still in the positive profit side or less loss amount side on his PnL. A casual gambling activity is acceptable if the person life is still normal.
I think most of the couple that experience this kind of this situation was they notice late that their partner is already addicted or the partner becomes addicted when they are already married. I said this because it’s very hard to socialize with gambling addicted person in able for him to have a successful love life. I’m still struggling on love life part even though I’m not gambling addict.