I don't know why they made a twist of the hero being female when MC visibly has strong affection, and then show her having son when she was away. Also she named him after Valmut, so they had strong feelings mutually despite being nemesis.
The only reason that comes to mind is that he actually is the father and got drunk and doesn't remember that she even is a woman. And the reason she left kid in Daycare is because he is half-demon. (or that she wants to cut ties with being a hero, since there are good demons like Valmut.)