Responses
Starting when does Ilay start acting like that though ?
And did Ilay burn the forest in the novel when Tai got kidnapped ? And the sex scene following that, the whole thing about Ilay claiming Tai as his property, did it happen ?
It would be good if that didnt happen because that was the best moment, in my opinion, to show how Ilay had started having feelings after Tai escaped the unhordo. But instead we got him going full psycho... and so i dont even see why he would ever change if he still hadnt after that

Guys, read the novel! (づ ̄ ³ ̄)づ
Poor Ilay is misunderstood.
In the novel, he wasn't aggressive with Taeu. And Taeu enjoys it a lot, so much so that he opens up more about his feelings with Ilay.
One of the reasons Tae hesitates to continue with Ilay is because Ilay shows him a lot of physical affection in bed.
I guess to give the comic some emotion, they left out parts and made Ilay look so rough... but he's not indifferent at all, or unconcerned about hurting Tae. Ilay hates hurting Tae, so much so that he has nightmares and puts his life before Tae, hahaha. Ilay loves it when Tae shows affection, those hugs from Tae when he's comfortable in bed.