^^^ My SIL has a high-functioning son (now adult). Nowadays, he's generally ok...works, moved to another city, more or less looks after himself.
But he was pure hell to raise. Always in and out of specialists' offices, always at the school, always fighting for this or that for him, or fighting about this or that with him, and she was divorced from his dad and he took the stance of "whatever you say, I'm fighting you on it."
Even now, he's in his 20's, lives 1500 miles from either parent, but they still have to do stuff for him, long distance (make sure he does his taxes, help him find a car, etc). He's not 100% independent.
And there's no guarantee that you're done at 18. All my siblings have ongoing involvement with their adult kids. One kid is always broke and needs money. One kid is always in some kind of relationship drama, one kid was a holy terror bipolar drug addict and you just prayed he didn't show up at your house at 1AM on any given day (he did that to me, and I'm not even his dad), and they all have one or more reason to be on medication (anxiety, bipolar, other stuff) and it means there's always some kind of worry or disruption or worse going on.
Aside from total estrangement, once you have a kid, that shit is for life. For life!
"There is no bad weather, only bad clothes." - Unknown