There are too many cop outs here. He leaves her for the commoner, but the demon had the power to brainwash. The commoner girl was actually a demon in the first place. It being all his plan. She says plainly that their relationship was combative, that she really didn't feel much for him in the first place and he showed no sign of loving her even before the commoner showed up. She was even investigating more out of curiosity than anything else. Lastly, her not having any trauma towards either of them.
I can't remember what story it was, but there was one where the girl flat out refuses to be anywhere near the guy that killed the MC, despite previously loving him and a lot of the circumstances leading to her death not being his fault. That is how you handle that level of trauma. I know it is a bit much for a oneshot for an anthology, but the goals of these things is to get people interested in the idea, and this one is just no good, imo. Even if you extended out the story to flesh things out, besides getting the people interpreting very annoying interactions as yuri to have even more fuel, it would just not work because there are too many cop outs.