In the case, at worst, it is a ruined relationship and wedding.
The lesson here is to always be sure we know our partner and what they are capable of for the sake of money...
This is true as a lesson to take from this story. She doesn't know the would be husband because if she does then she wouldn't have allowed him to have access to the money not to talk of using $5,000 for gambling. It is an addict that is likely to take that as a chance because a new player would be scared of losing but an addict will see it as an opportunity that has been presented to him.
She doesn't know what character he could display and probably he has been hiding his gambling addiction away from her.
Well, I am not sure we can certainly talk about a person addicted to gambling, because in my opinion if he was actually addicted, he would have gambled away that money before and would not have waited for it to reach that amount or even provided up to the 40% of the total wedding savings.
If I had to guess (because I am not an expert and I do not the whole context of the man's situation) it is probable he started to gamble quite recently when they already had that amount saved, and quickly started to chase losses with his own money, when his personal money was gone, he could not help but use those bucks they had saved for their special day.
If he was honest to his girlfriend and handed over those savings to her instead, he could have saved their relationship.