Gitae

For those who don't remember who Gitae is, he is one of Dohu's high school bullies. He was first introduced in chapter 54 where he faked an apology to Dohu because he didn't want his bullying past to affect his acting career. He later reappeared in school festival where he openly mocked Dohu for being emotionless, and that upset Juheon.

In any case, I don't think Gitae will be the third party or second love interest. Juheon has seen Gitae mock Dohu, and Dohu is unlikely to want to interact with his bully. Instead, Gitae's role is likely going to be one of the actors vying for the same acting role that Juheon has now, and he is going to sabotage it, which may prompt Dohu's interference. It's also possible that Juheon may learn more about Dohu being bullied in his high school days through Gitae since Gitae is such a chatterbox. He is bound to talk crap about Dohu again eventually.