Pretty much Yuwon had a head injury from a hit and run and his memories got switched. Dohun was never the one being bullied it was Yuwon all along, everything we say that happened to Dohun was actually Yuwon. The first season was from Yuwon's pov, the second season is from Dohun's pov. Dohun's brother is the one who hit Yuwon. I tried to be as clear as I could but I don't usually answer these :>

I kinda give up on understanding the second season so if someone with a good heart has the time to explain what is going on i would be very very happy. Thank you