How do I block my ex when I keep flirting with them?

I don’t know what to do? Idrk what to say in honesty I just need help, like actual help, I’ve asked a few friends and they all say to just block and move on but I’m not that type of person. I keep flirting with my ex and I don’t know how to actually do it and move on, it’s obviously just a case of “oh block them easy lmao” but I never know how to, whenever I try to distance myself it’s always a “you’ve change, stop being nonchalant” or “if you don’t want to be friends then just say it.” And I always fold and back to square one. I would stay with them but they’re poly and I’m not, and if we were to even date it’s just a self destruction thing and would never work out. I don’t know what to do I genuinely need help because I know I’m digging myself into a hole where im just going to start flirting with them again and I don’t want that, and I n is this is fully my own fault aswell.