Hello, i'm developing a turn based game where you can bet against your opponent, if you win you earn back your money and opponents money, if you loose the opponent gets all. So, I want this project work only with cryptocurrencies, but i'm facing a lot of problems:

1. People need to deposit money to the site, and when the start a game they decide how much to bet and then start to pay:
Problem: People dont like to deposit money on sites.

My solution: Users would deposit money on site on an address, I would give him the ability to download the private key of the wallet, but that comes with another problem:

If a user starts a game and bet 10$, since he has access to the wallet before the game ends he could just send the money elsewhere and scam the system. My solution:

Send bet amount before he starts a game to a newly temporal created wallet only for that purpose, but that's comes with another problem:

Speed, and fees,  bitcoin is slow, cryptos are not that fast.

So how could I solve this problem, giving the user the ability to download his private key but "freezing" the money for a bet.

The easiest solution is to not let the user download the private key, but i won't scam them and I want them to feel comfortable. I just need a form to freeze the money used in a game,

Any advice?