"I look at my tiny son and just think there isn't a thing I wouldn't do for him.
Give up the weed and kick your partner out. Start with that."
This x million!! You are putting this alky junkie ahead of your sons needs. You've already shown your son is not your priority and he should be.
I'm the child and niece of alcoholics, I've lost someone I was very close to to heroin. They all did rehab several times. Only one has been successful because they WANTED to do it! My father only doesn't drink now as he is physically unable to leave the house and nobody will buy it for him, he resents them every day for it and says so! My uncle has been sober 20 years, has little time for his brother (my father).
Addicts will not recover until they truly accept they are addicts, they are not in control of what they are addicted to and they and they alone are responsible for their own recovery.
Your sons father is none of these! He is not in recovery he and you are in denial. I too think in less than 6 months (actually 3 more likely) he will be back on the booze and whatever else he abuses. I too believe you also smoke cannabis. I am not of the view that ' a couple of joints is harmless' I have seen people have psychosis, and addiction issues with cannabis plus be more likely to have issues with other substances. I also don't think drinking often is responsible.
As pps have said you have been assigned a social worker because people with more sense than you or your sons father realise your son is not in a safe or sensible environment.
"OP, make friends with that social worker, you're going to be seeing lots more of her the way you are going." Definitely!
If you are smoking cannabis stop! Repeat get rid of sons father out of your home and your lives until he is genuinely in recovery and has been for a decent length of time!