@middling - I could write a ton on this topic. Kiddo is an only child, and we are incredibly close. Letting him go was brutal. But it was also the best decision we have made as parents. No regrets, even though I miss him every day. It helps knowing he is thriving in a way he couldn’t at home.
No one can tell you what is best for your family. I will repeat the wisdom of another parent of an incredibly close family: “It takes a lot of love to let your kid go to boarding school. A LOT of love.”
ETA: if that parent’s family is anything to go by, they are still very close with their kids (and now grandkids) 30 years later. This is 3 years (admittedly important ones) in a lifetime.