I wish people would’nt bother with these blaming and shaming comments. OP isn’t responsible for the lies her partner and his ex chose to use in managing their crappy relationship. There is nothing she could have done or said that would have changed this long standing pattern of aggression and avoidance between the SS’s actual parents.
The boy isn’t a heroic victim here—at least not if the OP. He’s just a resentful teen who can’t act out his rage and need for control on anyone but OP and her daughter. That isn’t because they are more at fault. Its just because they are vulnerable to the boy’s leverage (rage, unpleasant behavior, extortionate threats) which he can use against his father but not his mother.
The boy needs loving limits to his destructive, spiteful, rage. But he won’t get them from his spineless father. He only knows how to threaten withdrawal as that us what he kearned from his biological parents. OP can’t change this pattern but it’s not her fault.
Unfortunately it is what it is. If your so called partner doesn’t care to secure your safety and housing then he isn’t really your partner. He just played one for eight years when it was convenient.
Here on mumsnet no adult human is ever thought to reliably care for another person and her child for very long. The dependent partner is always held to be at fault for her poverty, disabled child, fragile circumstances.
Don’t look for sympathetic or thoughtful responses to this problem here. Just realize that your partner is not concerned to protect you or your dd.