Complex sentence: Ha-joon also has anger management issues and considers Kim Yeol his only true friend, but he, too, begins to regard Kang Yeon-doo as his true friend after he received help from her, and he even developed feelings for her.
Split into simpler sentences: Ha-joon also has anger management issues and considers Kim Yeol his only true friend. But he too, begins to regard Kang Yeon-doo as his true friend after he received help from her, and even develop feelings for her.