So, the hero is aware of the demon queen's desire for intimacy with him, and can become a completely different person who will enjoy looking at other women, and he's basically sworn marriage vows... but he's still going to leave the demon queen hanging like a knob.
Why can't these stories stop degrading themselves with artificial drama and poor writing when it comes to romance? Maybe Miyazaki was right, about animators (and, I'll add, artists) not living life enough and spending far too much time in the anime culture. They don't know how to write realistic relationships anymore.