Better to prevent and stop if possible before it's too late, depression is a possible outcome of what you did especially when you are not ready to lose a lot of money and you are using this venue to try making some, it's much better to play and use the money that you are willing to let go and have that kind of mentality to quit your way once you already suffer from losses that you set as limit before stepping inside this venue, otherwise you will suffer if you continue chasing your losses as your chance to recover most of the time is next to impossible.
What he should do like that, it's better to prevent it before it's too late, but maybe what he did before was that he lost control when gambling, spending a lot of money and chasing the winnings or chasing the losses he had earned. Yes, depression in gambling because it could be caused by that and when he loses at gambling he doesn't have a strong mentality so he can't accept it if his money runs out and his depression or emotions appear suddenly. Agree with you, before entering the world of gambling, it's a good idea to have money and time limits, the goal is so that when you lose, you don't lose much and you don't need to chase after your losses, because you only lose a little money.
You only lose the amount that you are willing to let go and not to have that mentality to chase the money, but to accept the fact that you are inside gambling and there's always a big chance of losing your money. With that anticipation, you can limit yourself and not to drive your way in aggressively trying to win back.
With a good acceptance, the chance of losing control and losing a lot of money is not as high compared to those who don't have any set limitation and just gamble their way inside the casino.