Based on how this chapter has gone and the current cover for the volume/series I'm going to assume the Demon Lord either is a wife or has a wife.
If she is a wife then she's stealing other wives husband's as a way to try and fill the void hers left.
Honestly I'm more just wondering how the Husband's are gonna end up. Cause the wife charm breaks if they die and I assume also if they divorce, and based on how that Merchant wife reacted once the charm lost its effect you'd have to wonder if any of their feelings are real or not.
Yuuto seems to be the unintentional villain of the story and I have to question if he even considers it wrong to sleep with another man's wife like what happened to him.
Realistically I know it's just funny ha ha NTR joke series but there's depth here should we ever get to a point like that.