Theres are a lot of questions right here, like who made the bet only the guy?, the girl?, or both of them, also is which money they use, can be argued with this kind of scenario. Still, it depends on the winner because they are just dating there's no responsibility for each other unless they are married, to be quite fair I guess that split is the best decision but imagine they keep dating normally. They won money split the money and got separated.
But what the OP shows is that they are a couple, which basically what one of them has belongs to both of them, the term is already embedded by itself if you have a partner, whichever money is used to make a bet then the result must be the choice of both, but this becomes complicated when it comes to money and feelings and also rights, sometimes the claims on each partner are different even though they have a bond in a dating relationship, however the basis is mutual sharing, that's what might be debated.
It's ridiculous when it comes to relationships and when it comes to money they split up, isn't that illogical? I say why don't they enjoy it together?
I agree even if they are dating there is a long relationship between them and the relationship is not built in a day. Even if they wanted to they could subdivide everything together. Separation for money is really bad. It is not always right to build relationships with money people prosper through good relationships. The amount of money they have won will end one day. If they were together the relationship would have been better and luckily they would have had a chance to win more.