OP, I really don't mean to drag back other threads in any kind of horrible way, but didn't you start one about supply teaching work? Aren't you recently separated, six months pregnant, and financially struggling?
Again -- really, not muckraking here. It was just something that chimed with me, because my mother was in a very similar position when she and my father divorced. She wasn't pregnant, but I was seven, my sister was a toddler, and she was a former teacher who'd left work to be a SAHM. When my father left, she had no money, no job, and not even a car (big issue in a rural area).
It was (understatement) a really difficult time. I was an introverted child, and I didn't like school, but I was never given the option of leaving, and now in retrospect I'm glad of that. Without realising, I had taken so much of the household anxiety on my shoulders, and staying at home would have really exacerbated that. I worried so much about my mother, and how we were going to manage.
I think the eldest child, when one parent leaves, will often place a lot of pressure on themselves to 'step up'. Even if they can't practically do anything (and probably in part because of this inability to really help) they will feel a great respnsibility towards their mother and younger sibling/s. I completely understand that your maternal instinct is telling you to draw your son closer to protect him, but IMHO he needs other, more impartial avenues of support (I really hope you will seek professional help for him), plus a certain continuity. It sounds like everything has changed very quickly, and that more huge changes are coming soon new baby, moving home and school and I really think there's something to be said for maintaining a routine, even if it's not an especially happy one.
If you're not the poster I think you are, then I really apologise!