
Hear me out.
Taeui was always attracted to Ilay even when they were in unhrdo. He says Ilay isn't his type but he always put emphasis to ilay's looks and even his hands. That's why he felt the most betrayed when Ilay hurt him. And he always gave way to Ilay what he wouldn't tolerate with Xinlu (that is being dominated). And because he is attracted to Ilay, he always wanted to find a humane part in Ilay so he could rationalize and validate his feelings.
Gosh I started this thinking it was complete. It was not...