Terrible idea. And it's even worse if "cards" doesn't mean Poker. But I'll assume it's Poker.
The first red flag is that he'd need you to cover the bills at first. That makes no sense. If someone is making enough at poker to turn pro, I can't think of any valid reason they couldn't contribute to the bills from Day 1 as a pro. Hypothetically if he were ready to go pro, he'd have already saved up a bankroll from his poker profits, which he'd use as his poker bankroll going forward, and he'd have no doubt that he'd continue profiting.
Another red flag is that you say he has to "try it out". One isn't ready to go pro if they're still in the trying phase. A sensible person doesn't go pro until their sample size is large enough to rule out the possibility that they've simply been lucky. (By the way, 3 weeks is way too small of a sample size.) He should already know his hourly profit rate within several dollars and the low end of it should be good. He should have a poker log with all of his sessions containing the net profit and the start/end time, which he should be willing to show you.
He shouldn't quit his job yet (if ever); he can play in his free time and build his sample size (and poker bankroll, if he's actually cut out for it). IMO he's unlikely to succeed if this stuff isn't already obvious to him.
Plus if we're to take literally that he has only been "breaking even" so far, then how in the world is this even a discussion? How does one make a living earning $0/hr?
If you were to ask this on a poker forum or even r/poker, the answers you get wouldn't be any different.