Hey @Goldenrod_Ferret
This is a great question that I think a lot of people in your shoes have. First of all, I am sorry to hear you have grown apart, and it also really hurts my heart to hear that he experiences teasing. Unfortunately, many young people are not welcoming of neurodivergent people, which makes it very difficult.
My experience and suggestions
I have worked with a few people with ASD in the past, tutoring them to be specific. But a lot of the time it wasn't even tutoring, I was more just having a conversation with them.
Activities
I find it easier to find what the neurodivergent person is interested in and go with that. What does your brother like doing? Are these activities that you can go along with or maybe have a conversation with? I used to talk to one student for hours about their Minecraft world, we really bonded over that.
Just being present
A lot of the time in ASD and ADHD populations, physical touch and activity are not something these people enjoy or partake in (as I am sure you know). I sometimes just sat next to one of my students with ASD/ID, kind of doing my thing but physically being there in the moment with them. This is dependent on your brother, but I think non-verbal support is valued and important. Just being with someone with ASD/ID I have found may even relax or prompt conversations of their interest. Might be a really good way to get the ball rolling.
Conversation Topic
While it is so disheartening to hear about your brother's teasing, he may not really want to talk about it. So definitely don't force it if he doesn't want to. Instead, I have found talking about topics of their interest (as mentioned above) is quite helpful in buffering the effects of bullying and teasing. Provide strong social support, and show him you care. Maybe as your relationship builds up again, you might find it suitable to directly ask about it.
In summary
1. Talk and if you can partake in his interests
2. See if you can start doing some of your work/activities around him, be present
3. Focus on supporting his life in other aspects - The trust will come
At the end of the day, you know your brother better than anyone on the internet. Do what you think is right :).
Best of luck
