Kotoha:

Arata: ...they're-

Kotoha, Kadowaki, Kanate, and Ginchi

Me making a list of all of his kids: wait Lilynette already has a dad

Chapter 200 has him faced with the same situation he was faced with in the beginning: A close friend of his joins Kadowaki, betrays him (Suguru through destroying his desk and joining Kadowaki's trash talking; Kanate by trying to fight him and get him to submit), and says they were never friends.

Although the situation is different - Suguru was pressured to betray him under threat of bullying, unknown to Arata; Kanate joined Kadowaki willingly and then was brainwashed by Ikisu - the idea of Arata being faced with a friend who has betrayed them and claimed they were never friends is the same.

But how he handles Kanate's situations shows how much he has grown since Suguru.

When faced with Suguru's betrayal, he doesn't stop to think about why Suguru would betray him. He just runs. He breaks. He figures of course he would betray me, everyone betrays everyone, no one can be trusted. He doesn't fight back or confront anyone. He just gives in.

When faced with Kanate's betrayal, he immediately figures out Kanate is not acting this way willingly - he's under someone else's control. And even when he realizes Kanate's feelings of inferiority are still real, he calls bullshit on Kanate claiming they were never friends. He fights back, because he knows his friend. Kanate would never act like this, Kanate would never willingly betray him.