My kids are very different.
One has a BFF that's his tride and true. Attached at the hip best buddies. A few bumps now and then but over all a long standing good relationship.
The other one has a new BFF every couple of weeks. He talks about his pal, draws pictures and writes their names over their little figures, etc. When I ask what happened to the old BFF (when he starts talking about a new one) he says: "We're taking a break." When I whose decision it was he always says it was his and not the friend's. I don't think it's a drama or fighting issue because he tells stories about what happens at school all the time and I think I'd be hearing about drama from either him or his teacher. Also... he's not my dramatic kid - the other one is.
My curiosity is if there is a "norm" when it comes to friendships in the pre-K or K age.
Thoughts or feedback?
FWIW - at school everyone is described as "friend" and we don't actually use the words "Best friend" - just using it here for clarification.
Re: Talk to me about friendships...
I think every kid is different. My DD has a new BFF - - not every couple of weeks, but every school year. She has always been friendly with lots of different kids.
DS is completely the opposite. He has one BFF, and a "top 4" and it has not changed.
If I were in your shoes, I would allow your DS to choose whoever he wants as his bff, but I would make sure he spreads his playdates around ("Billy came over to our house last time, why don't we invite Jason this time?"). And let him know that even if he has one bestie, he can have lots of good friends. Liking one person doesn't mean that the other friends aren't important to you.
It took both of my kids until they were at least 5, maybe closer to age 6 to have a "best friend" in the classical sense you think of during childhood.
Before that age, they didn't know themselves well enough to find and bond with another kid that had the same interests, etc. They would say "so-and-so is my best friend" and it would clearly mean "I played with so-and-so today."
Additionally, my kids are very different socially. DD tends to have a small number of very loyal friends who are a lot like her. She enjoys getting together outside of school, but is also happy to do her own thing for a while. DS's social circle is a little wider, both in terms of number of kids and in their personalities. He always wants to have playdates and visit friends. He's always interested in meeting new kids and having them over to play. Summer is hard for him because he doesn't see his buddies much.
In watching my kids and their classmates during pre-K/K, there were always a few kids who were like your son and his best friend: joined at the hip. They always played together, etc. Then there were kids in preschool/kindergarten who would play with pretty much anyone, and their companions changed all the time.
I used to worry about my DD a little, and wonder if she was getting enough of a social life. But I have learned to stop worrying about it so much. Her social life is what's right for her; she's happy with it.
My twins have very different personalities which I think has lended itself to one having a best friend and the other being friends with everyone in his class and switching best friends routinely.
My son with the long term (the last 2 years he has been at this school) BFF is introverted and prefers hanging out alone or 1:1. My other son is extremely extroverted and moves around to various social groups at school (and hence has lots of BFF that change.)