I know of a lot more, but I'm so hella lazy so km only going to do 4.

4. Jiho/Nacseo (his name at the time) & Namjoon/Runch Randa lol

These two have been friends for, by my guesses, about 10 or 11 years. 

3. Wheein & Hwasa

Idk how many years, but they've been best friends since middle school.

2. Taemin, Kai & Ravi

I know Taemin and Kai have been friends for, like, forever, but Ravi became their friend in trainee days I think?

1. Jiho & Kyung

These two are the closest of friends. Which makes perfect sense as they have been friends for, by fans' guesses, nearly 16 or 17 years. 

That was all I could think of lmao I'm so lazy