I think the curse might be "a new woman each day" and not have a technicality like "different from only the previous day." Just my interpretation though.
Twist ending: he gets bored of it, hypnotizes a girl to be his wife and they grow old together. The "hook" can be they have a kid and it's implied the kid has hypnosis powers too.
Yeah, I found this to be an interesting conundrum to ponder since on page 7 he notes that he'd have to find a woman and immediately rape her but then says "no, rape is wrong and as a human being I can't stoop that low." So it makes one wonder if he did resort to rape every day just to live, would he even be okay with his existence? Or would he have to forgo an aspect of his humanity to try and live with himself?
This reminded me of Rance in several ways from the MC to the bad guy who was similar to the bad guy in Rance 2 to the ending with space which was like a reference to Daiteikoku which itself had a cameo of Rance in space.
She taunted him and said “wow, look at you sleeping with a girl you’re not even in a relationship with.” And he said “Aren’t you just as bad?” implying that she is also fucking someone she’s not in a relationship with. It’s just pot calling the kettle black.