Maybe consider yourself in JY's place and think if you'll have "a single shred of empathy" for the person…
I don't actually blame him either, but I've just become completely disconnected from him emotionally. I can't feel his pain anymore, and I find it impossible to empathize with the pain of a cruel man. That's it. And his cruelty isn't about his harsh words, honestly.
Maybe consider yourself in JY's place and think if you'll have "a single shred of empathy" for the person…
Even in that exact scenario, yes, believe I would still hold onto a shred of empathy. Empathy isn't driven by pure logic, or calculated justifications, it's an instinct, when you see someone suffering right in front of you, feeling completely okay with it points to a serious emotional disconnect, especially when that person was your close friend. And I don't mean that Jeong yo's actions aren't justified, at least within his own mind. I just personally can no longer stand his character or find any emotional connection with him. Understanding someone's trauma doesn't mean I am obligated to tolerate their cruelty.
Im sorry but I've lost all sympathy for Jeong yo, while he definitely went through a lot, it doesn't justify how evil he has become, even if he has his reasons, but how he could hurt Pio without a single shred of empathy? He has become completely blinded
K-Drama 
And his cruelty isn't about his harsh words, honestly.