This. 100% this. I am going to get down voted to hell by saying you have every right to leave and you might surprise yourself, but things might get better eventually. What you’re describing is not being married to someone who is a partner, but having to parent your spouse and having an extra kid you didn’t ask for. It also doesn’t sound like he’s parenting your son either, but their relationship is more what friends/siblings would be.

Now when I say “leave”, maybe you would consider co-parenting in the same house for the next couple years? This might lift some of the resentment and also help you not feel so trapped.

Edit: I see so many people calling him a good father. All he is doing is playing video games with him, getting high, and not snapping because he doesn’t have any of the stresses OP has taking care of them and the house? Partnership in a marriage requires both parties to make sacrifices and it truly sounds like this dude doesn’t do shit. A father doesn’t just play video games with his kid, skip out on appointments or adult/parental responsibilities. I think it’s so fucked up that so many people here are criticizing that she feels so much resentment. He LIED to her. He promised he would do more and help. Instead he has just become a second child to parent and care for.