OP, you don't have to live like this. It sounds like you've been really ground down. One thing I noticed is that you've got some rules in mind that you think you're meant to keep, eg you made your bed so you have to lie in it.
Whose rule is that and what does it mean? If your 'bed' is being a mum, isn't 'lying in it' about making the best life you can for you and your son?
I'm sorry you found it hard being in a single parent family but it is important to recognise that you can't undo the past by staying with this man. You won't be giving your son something that's somehow better just because he lives in the same building as his dad.
You wonder if your dad cares about you and that is an awful way to feel but that doesn't mean it's better for your DS to live with his dad or that it will somehow undo the past. His dad is not able to care for him or you in the way that is needed.
And when your son grows up and asks why you didn't leave, what are you going to tell him? That you had made your bed and had to lie in it? That you wanted to continue the charade of a nuclear family?
Children need to play with toys. And you have needs too. Please don't choose this life for you and your son; because you do have choices. And while I think there have been some scare mongering posts, it is true that the lack of stimulation would be a child protection issue.
You didn't make your bed, OP. You made your son. He needs you to make a better bed for both of you.