Good luck Speechie. It's the same for us - I'm DS7' best buddy since forever. But things do change. Take heart!
Actually, that's how we started homeschooling - I finally quit my job and pulled DS out of Kindy when he turned 5 because he didn't have friends and wasn't learning anything. How he loved the isolation! I spent most of my energy arranging playdates which never stuck. Then last year just before he started Gr 1, we lucked out when he met a very likely PG 9yo. They're very different, yet they connect. DS says he's the only one he can really talk to. DS became very sociable in the two years we homeschooled btw and now has quite a few of what he calls "physical activity" friends, but he'll opt not to see them when he has an interesting project at hand. This recent school holidays, he was invited to a birthday party by a classmate - he refused to go. "No need whatsoever", was his explanation.
Just for laughs, I remember my son meeting a bunch of very rowdy 6yos at a party when he was that age, becoming rather crazy and flippant himself that day, and then saying privately as we were going home - "so now I know how 6yos truly behave!"