I think that expecting an 18yo to instantly have perfect boundaries with their mother is out of line even if everything is exactly as LW1 reported it. Sometimes it happens, but you can't expect it. ESPECIALLY if the other sibling cut off the mom: the pressure of "YOU"RE ALL I HAVE LEFT" can be huge.

Yeah, exactly. It feels like LW's seeing the son's behaviour as a continuation of his mum's - "Son got better at lying to me" - when it's vastly more likely he's a victim of his mother's. The kid does need some reliable help imo, even if he fucked up here, especially given the wrecks and loss of licence as he was growing up - it doesn't sound like a stable situation.