I understand this. And I miss my son sometimes too. He does the same thing he’s 27 years old. He does come out of his room to talk to me once in a while to eat. We’ve set times where we get together and do activities. Like we read together we try to do it a few times a week. And we play a game of Uno together once a week. I know it’s not much but it’s a lot when your son spends his time in his room like ours does. 
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“We are all creatures of our upbringings, our cultures, our genes, our neurochemistry, and, not least, our brains. There is no one normal brain, and no one normal mind.”
~ Oliver Sacks (Neurologist & Author)