Toru Ishikawa and Izumi Miyamura were the types of friends who don’t show much affection on the outside but have it inside. In HoriMiya they both had many scenes when they were talking about themselves and their friendship. In the anime, they’d fight but also apologize obediently.
How was their friendship?
Miyamura and Ishikawa’s friendship was a friendship where they both didn't show love even though they had. At first, Ishikawa found him annoying as Miyamura was getting closer to Hori and as Ishikawa had feelings for her he was jealous and annoyed at the same time. Miyamura was shy and unsociable, so when he got to know that Ishikawa had feelings for her he started avoiding Hori for Ishikawa’s sake.
Ishikawa sees Miyamura as a close friend as well as a rival in love. Even though he seems to have given up on Hori so that Miyamura can pursue her. Ishikawa unintentionally hears a conversation between Sakura and Remi, where he discovers that Hori had a crush on Miyamura. Despite the rivalry, they were quite close. After Hori, Miyamura’s closest friend was Ishikawa.
He was the second person who saw Miyamura’s tattoos and piercings. They shared a very simple yet interesting friendship. They both even fought among themselves because they started arguing about Hori and they ended up hitting themselves, though Miyamura was able to win the fight. Later in school after explaining their fight to Yuki and Hori, they apologized to each other and became friends as they were.
Miyamura was able to tell his secrets to Ishikawa without any hesitation and also able to understand each other’s feelings and emotions. Ishikawa also claims that the way Miyamura ties up his hair he looks as pretty as another girl. From this, Miyamura blushes and Ishikawa cries that he makes him annoyed. This also shows that he secretly adores Miyamura’s looks and the way he ties up his hair.

Did jealousy became a hindrance in their Friendship?
Jealousy and friendship both can be seen in Miyamura and Ishikawa’s relationship. They even shared a moment when they both asked about their thoughts on themselves. They sincerely talked about each other and Miyamura felt a strike of happiness when he was aware of the fact that now he has a friend with whom he can spend time and have fun.
Miyamura after befriending Hori he gets himself a group where he can call them his friends. He was extremely happy about the situation and the moments he was making day by day with his friends. Even though he was aware of the fact that Ishikawa feels jealous of him, he didn’t stop talking to Ishikawa but they only became close friends. Also after coming to know that Miyamura and Hori were now in a relationship, he genuinely accepts them as together and keeps supporting them. Ishikawa does feel jealous many times as the girl he likes is with someone else.
The part when Ishikawa had dreams about him killing Miyamura seems to be normal as he often feels annoyed by him since Miyamura started talking to Hori and also visiting her house often.

Where did their friendship ended?
Toru seems to have this feeling as he feels confused and depressed until he seems to get attracted to another girl, Yuki. Miyamura knew about the affection Yuki and Ishiwkawa started to show even though they were not aware of it, Miyamura supported their relationship as much as they supported Miyamura and Hori’s relationship.
Miyamura and Ishikawa were kind of friends who get jealous and annoyed by each other many times but in the end, end up coming to each other. They showed secret affection to each other and showed many cute scenes where other students mistook them as couples.