Ooohhhh I didn't think this at first but it kinda makes sense now!
OMG
i was thinking the same thing, but tsugura said his best friend's name was "taguchi," and when saikawa and tsugura saw each other in the manga, they seemed to not know each other on a personal level... could still be a possibility, though! as far as we know, saikawa is living with his dad, so maybe something similar happened between his parents to cause them to split?
My brain literally went “forget taguc- who?” You’re theory makes the most sense a lot of sense or maybe we’re just over thinking it and Saikawa just doesn’t want to be hurt emotionally and stuff, but who knows! :)
I THINK THE ‘best friend’ WAS SAIKAWA AND THATS WHY HE DOESNT WANT SAYAMA HANGING WITH TSURUGA. Since his girlfriend already cheated on him with Tsuruga he doesn’t want to get hurt again so he’s avoiding Sayama.