He has OCD and ADHD, probably BPD, this behaviour is typical. As they get older many get worse and they tend to isolate and drive everyone away. There may be those that don’t. I am the last one left standing because my family member has driven everyone away. They do not get the help they need, the doctors do not seem to care. I see my FM when he's being reasonable, he has a caring side and is very intelligent, he has trigger points which I avoid, then he has a quite manic period, he says dreadful things, whatever I say is wrong and everything is my fault, I do not shout back, tell him when he's ready to talk I am here. More verbal abuse. So then he blocks me, sometimes for weeks, very often months, my life is so much easier then and I cannot tell you how much easier if I walked away.but I don’t as he just has me and he is so unhappy inside. Dread what will happen to him when I am not here he will have no one. You do not choose to be like the tortured soles they are. The family are the victims too so no wonder many cannot cope. Everyone tells me how its affected me and I tell them I will not ever turn my back on him just have distances. Eventual he gets in touch, usually some grand gesture, apologises and here we go again.
I know lots of lovely adult caring children, so this isn't the norm. Its mental illness.