Taeui like a broken record has cleared it up multiple times that he does not for one bit regret choosing to stay by Ilay's side.
Also here Alain being too self-aware of iltae's relationship wondering how someone with Ilay’s past can get access to ordinary happiness and roam freely while his victims suffered, as people like them (task force unit) are "not supposed" to get salvation due to their line of work; and also discreetly implying that Taeui succeeded where others failed as he literally humanized Ilay or at least made Ilay capable of living peacefully and Taeui does not deny that and simply accepts that Ilay did/does commit terrible acts and that consequences for his actions are unavoidable, yet he still will continue to choose Ilay anyway.
Taeui says even Ilay himself knows that he’ll pay for his sins someday, but not like a legal punishment kind of way but more existential like loss or grief such as losing Taeui himself. It's very bittersweet to hear Taeuis response because he is admitting that loving Ilay means inheriting Ilay’s fate and that peace for them was never meant to last.












