If his cousin was a long-time gambler so it means he passed massive heavy experienced which he has control of his gambling.
But the wrong move is, why he did not let know his fiance about his gambling activity and tell her about that he has control over it and nothing to worry. Girls have always that kind of attitude, trying to control someone especially if they know the outcome, but if you are an experienced gambler, you can tell her that you are not addicted and tell her that gambling is one of your habits. If you can explain it very well, then, there is no problem.
the final decision will be on his fiancee because for sure she already knows that being a gambler is hard to get away from. it would take time for her to see if he is indeed stopping his gambling activities. they both need to sit down in this situation as they are planning for their future life together. it will be the cause of their marital problems later on if they haven't come up with an agreement with this aspect.
but since its been said that the guy isnt really that addicted on gambling and turns out to be profitable then i dont see that it is really that wrong to continue on what he's doing.Also, it is really understandable
on what the girl is been feeling out because we are not that dumb not to see on what are the possible circumstances might be faced up ahead if ever his future husband would be addicted into it.