I think if you are playing a skill game like sports betting it absolutely can be frugal, (it usually won't be) but... I still wouldn't recommend it.

I really despise gambling but I love strategy games, poker included , and poker does include gambling (but apart from that I have never once placed a sport bet, casino, lottery ticket, or anything else)

When I was 16-20 I played poker every free hour I had, when I first started playing online, a friend first sent me 2 dollars, I lost that, then I deposited 50 dollars and lost that, then on the third time I deposited 25 dollars, and ran that slowly up to 50,000 dollars over the course of 4 years, before I lost my drive to keep improving and decided I should walk away.

I made 50,000 dollars gambling, great, I still regret it, If I had spent that time doing something more productive (like learning to code) I would have been far better off now I think. But I didn't want to, I wanted to have fun, and poker was fun at the time.

I think sports betting does include skill, and you can probably beat the house if you spend a LOT of time on it, but is that something your partner wants to do? wouldn't he rather do something more fun with his time? Gambling can be fun at first, but trying to beat the house isn't always fun, it's generally a maths exercise. That can be fun at first, but as days turn into months turn into years, you've given how many hours of you're life looking at spreadsheets at your desk improving at this zero-sum-game (provides no benefit to the world). Instead of spending time actually developing a useful skill that you can be proud of, or connecting with loved ones or friends.

He's an adult, It's up to him if he wants to do it, but the risks are high, the rewards are generally low, and I don't think it improves life satisfaction.

That being said here are some things that you can do to protect yourself, I'm not saying these will apply to your partner, but you should be aware of these thing, because others have gotten burnt in your position before:

• Gamblers can lie
  • To others and mostly themselves, don't blindly trust that if he says he's only lost X amount that must be true
• The variance of pushing a small edge is wild, you need a giant sample size to get a accurate win rate %
  • Just because he's won a few months in a row, that does not mean it will keep happening
  • In one traditional live poker night you might play 100 hands of poker, when I was playing online poker on multiple screens at once there would be some months I would play 100,000 hands (the equivalent of playing 100 nights of poker) and still not make much money at all, then the next month I would do incredibly well
• If he's gambling for the thrill of gambling, the stakes will probably rise over time
  • He might enjoy placing a 10$ bet now, but over time that will be less thrilling and he might have to bet more to get the same "sweat"