beta
My best guess is that the brother was obsessed with Won. Think back to the crazed look on his face when he was choking the dude while DTD when the MC caught him before moving out.
The uke is gorgeous, and the brother obv tried hard to befriend him, even when he was being rejected. The uke was also very obv not happy with the touchiness from the brother. I think the brother became obsessed, and then the uke ended up with feelings for Jinha. So, he secluded the uke away from everyone, therefore losing contact with his friends.
When the uke & Jinha ended up meeting/being suspected/actually doing something, the brother beat the shit out of Jinha or designed an accident, hence the hospital accident. Then the uke finally decided to leave, he punished him by unaliving himself.
So, the uke is being honest, but he's controlling and likes rough play bc he's been abused mentally/emotionally, etc. for so long. Monkey see, monkey do. It's also why he tolerated the abusive behavior from Jinha and the reciprocity, and is afraid of being alone.
((Or the uke is crazy, orchestrated the accident for Jinha, and is now using him as a replacement. Doesn't fit nearly as well as the first option, though))