If they cannot fix that problem and don't talk about it. The relationship is at risk and likely to get separated. But even if the other one is a gambler, they can have a setup wherein the gambler can continue to do it but with limit. Everything can be done in talks if they have to do it. For as long as they understand each other and there's a limit to how much one can gamble to, it should work fine.
Theoretically, this is a nice approach, but is this what happen in real life!? I don't think so. It's always a debate on whose wrong and whose right. The gambler partner argue that this is his right to chose the way he prefer to entertain as long he fulfill all his missions as a family member. And the other partner also argue that this is a risky practice that can develop to be a pathological habit even he practice it with moderation. Sometimes it reaches an end even before without the family life get harmed.