Responses
I don't think demon-val (deamon uke) likes it either. Seeing as Hall (seme) was first with the demon form before he was with the actual prince. As we can see that is why demon prince val is so angry in the recent chapters.
Right because if you look at it that way, Havi is cheating on the demon since the demon is the one he slept with first. He didn't even like Vald for a long time.
I don't like it. When the seme is sleeping with the devil-version of the uke, it feels like he is cheating. The uke and the devil are not the same person, they are only sharing the same body.