I'm part way through watching it, and am in similar situation to Flo with my DS now 18. Despite having a diagnosis of ASD at age four, the support he got through school etc lessened as he got older, and he was expected to cope more. I don't think anyone thought Autism was something you grow out of, I think it was about cuts to any of the provisions that are supposed to help, and an emphasis by the schools on their league tables.
This time last year he got an emergency CAMHS appointment when he was 17, after I intervened in his suicide attempt. At the meeting with them he spoke about suicide, and was clearly psychotic, talking about a spectre in the room telling him to kill himself. CAMHS discharged him. We had nothing, no help from anyone, despite me literally begging anyone and everyone for help in keeping him alive.
I went back again to my GP asking for an urgent CAMHS referral again. Six months later I got a letter through saying he could have an appointment, but as he had turned 18 he no longer qualified. It was almost funny in its absurdity.
In the end I paid for him to been seen privately and got him medicated. But even that wasn't enough and we are all still hanging on by a thread.