Because you are on 3rd place he's in 2nd place that's why...
You are like this Hinata first,Sasuke second,You 3rd,Karin 4
He's like this Hinata first,main second,sasuke 3rd,karin 4

i battled him the same time, with the same formation. his main, even his sasuke is ahead of me. I don't get why? I've been asking that question since day 1

His Sasuke is also in position 3 so he can still be ahead of you. The only way to guarantee your main goes before Sasuke is to put him in position 2. In other words, move Cursed Sasuke back one space.

We battled with the same formation but still he goes first. How can you tell what happens with that?

You're looking for whatever the fourth tiebreaker is. Don't rightly know that one. Some say it's whoever loads first.

Attack speed -> Move order -> Initiative -> ???

So crappy connections won't stand a chance in tiebreakers? Mehh that rarely happen anyway but there should be justification.

Anyway, attack speed is the one you're talking about right? Or that is different?

No, attack speed is the first tiebreaker.

Prompt jutsu go before Normal jutsu or Standard attacks.

What stat defines attack speed and where can you see that in game?

The mentioned attack speed by Kyutaru tells if the skill is prompt or not. Of course the prompt skill has a faster "attack speed" compared to non-prompt skills.

sweet. Thanks for the clarification!

Also prompt mystery allows you character to perform a standard attack, you can even cast a prompt mystery after you character did his standard standard attack in the same round while non prompt mystery remplace the ninja standard attack.