Sorry for the length. I could really do with some wisdom from mumsetters who have or have had children at boarding schools.
I'm a mum whose daughter had the choice between excellent local schools or an even more excellent boarding school. (In our US state they are actually ranked first and second.)
She was also very disorganised (probably ADHD but refuses to see a psychologist for a diagnosis) and I very much worried that she would not cope at boarding school.
She chose to apply, did a tour, said she had found her people, and was offered a place at 13, starting at 14. She went for four years.
In our situation (everyone is different) it helped her immensely, and our relationship improved enormously.
As it turned out, it was the perfect school for her. Because she was so much happier there, she was much happier in the rest of her life. Her relationship with everyone in the family got much better.
At graduation she wrote and delivered the valedictorian speech, in which she talked about how this particular school was where she found the right place to become herself - where she was entirely accepted.
She has since gone to university (she's in her second year) and we get on very well - she facetimes us a lot, texts with us all, and she's flying home for February break.
We did worry about letting her go much as you are worrying.
DH went to boarding school, and although he ended up loving it, he hated the first few years.
I worried that she wouldn't cope with getting up in time, being tidy, organising her schoolwork etc. As it turned out, being at boarding school helped her on all those fronts - because she wanted to be there, she learnt that she had to be organised, so she chose to learn how to do so.
It prepared her very well for university.
But that's just our experience. Your family is different, your son's school options are different, he has different needs.
No one can really tell you how it will work out.
I can tell you that my husband, his siblings, his parents, his cousins... pretty much everyone in his family went to boarding school, and they all continued to have good relationships with their families. But that doesn't mean everyone will.
Good luck with the decision. It is really difficult! I really struggled with it.