i thought he left cuz theres nothing more holding him there in the palace. he was there in the first place cuz he was captured and accused of that prince's death, out of spite he brought the witches with him to fall together. ryan saved him on that court so he could continue 'eating' him. after all thats done, he left cuz the witches are dead, trial is done and hes out of the death row, place just reminds him of his mother's burning and he prolly dislikes being fudged by ryan everytime.
I think he ran because he is afraid to kill the prince like he did with all the other men. I truly think that El has feelings for the prince, wither it is because their past as children or because El feels like the prince is the only one that ever wanted him as a person. El left because he was scared that he would either hurt the prince or the prince would hurt him.

why of all things.... " i like you"?
what is el trying to achieve? ryan being gentler and kinder to him? ryan being distracted and use the time to escape? he genuinely likes him? (doubt it),el trying to make an illusion that hes doing it with someone he loves so it wouldnt hurt as much? (but he has no heart, he killed all those men, i think hes numb)...WHY I LIKE YOUUUU?????? ╮( ̄▽ ̄)╭