You have to leave. I am so sorry. But you do. You deserve a better life and your children definitely do.
My uncle was a hopeless gambler, though ever hopeful. He was also very charming and a nice man which it sounds like your partner is not. That's not to say my uncle was a great prospect it's just that he was great company so long as you weren't married to him or didn't lend him any money you couldn't afford to lose.
He was almost a mirror image of my dad - both very good looking - but my dad, the younger brother, always had to look after him which cast my dad as the boring brother. My dad did a very good job of making sure his brother was looked after but never got hold of our money but it must have been exhausting and so unfair just like it must be for you.
A girlfriend with a small child from her previous relationship said to my mum: "I love him so much except for this. What should I do?" My mum, who really liked my uncle at a safe distance, said the girl had to leave. And she did.
Everyone can change their ways, of course they can. But they have to want to and I think gambling is one of the most pernicious addictions there is.
You can, with determination and support, avoid alcohol and drugs by changing your social life and your circle of friends. It's hard but it's do-able. But the encouragement to gamble is everywhere - even those adverts on TV and bus stops saying: "When the fun stops, stop" like it's easy for an addict to stop.
It intrudes on people's lives. You can't really not have a smartphone in 2023 because so much stuff is done online - banking, job applications etc. It's possible but it's restricting.
I don't gamble. Not for any moral reason, I'm just not interested. The last time was when the World Cup was held in Russia in 2018 and there was an office sweepstake which I noticed but didn't mention was organised by the biggest gambler in the office. It's always the way. It's a social thing but some people were buying more tickets at an affordable £5 a go (if you can afford £5 that is) because they got Costa Rica. I got Russia who who were knocked out in the first round I think.
But even so I still get ads on my Facebook because of something I must have said that the algorithm has picked up. I imagine someone who gambles gets loads of them every day and it must be so hard to resist.
I'm not making excuses for your partner. You should leave and you will have a much better life and so will your kids. I promise you. All I'm saying is that a gambling addiction is hard to escape. But you have to look after yourself and your children. Good luck, as gamblers often say. You can make your own luck.