I'm going to refuse to pay my ex child support
Why do you want to refuse to pay?
Because my ex wife blew all that money on her boyfriend.
It's wrong to refuse to pay that support. What you should do is report her to the authorities for not using that money on the child.
But if I pay then I don't have enough for my alcohol and weed.
It doesn't really matter because you are required by law to pay child support no matter what.