The money is not a college fund. Your customer's previously-held inaccurate predictions of the future turned out to be false. He changed his mind. Your assertion that it "is intended for paying for college" is false. It is intended for paying for roulette.
It is not your right to choose for others how they spend their money.
Stop trying to control other people because of your certainty in the belief that you know what's best for them.
It can be better to temporarily infringe someone's rights if it stops them from doing something that they will regret for the rest of their life.
No, this is false. You're incapable of guessing what other people may or may not regret with enough accuracy to use it as a justification for infringing upon the rights of others.
Furthermore, most are heavily influenced by societal norms and customs, making this even more dangerous a justification when used against the rights of those with eccentricities or nonstandard tastes or lifestyles.
It's never ok to infringe upon someone's rights.
A question: how do people find themselves "in the clutches of an addiction"? How do they escape? Could it possibly be their own free will to decide to smoke the first cigarette, or their individual decision to walk past the bar without going in, on their way home from AA?
Do you agree that it's right to have age restrictions for buying and selling alcohol?
You realise that many alcoholics start drinking when they're children?
People are social creatures. Trying to ignore that and treat everybody as isolated individuals ignores those.
Clearly it would be immoral for you to intentionally provide a source of liquidity for stolen goods. How does that show anything about your gambler?
Often legality and morality do align (but really not as often as you'd think), and this is fortunate, because it allows good people an easy mental short-cut for weighing one's actions based on legality (and punishment), as well as protecting the weaker-willed parts of society that often end up on the wrong end of moral decisions by people like sneak, who'd let people drink themselves to death because if everybody was completely free they'd surely decide out of their own free will to do what's best for them and nobody would ever prey on the weak-willed like that, ever.
How the hell would this be ethical, no matter how consensual and non-coercive it is?