My idea is He just using her for whatever reason. They already sleep together even if she barely know him for 3 months and before they even go steady. After he got what he want than he leaves Saena behind maybe without knowing that Saena pregnant with Kyoko. Feeling betrayed and since Saena have such high pride, I guess she didn't chase after him. Or it could be he knows about pregnancy and just being an asshole. Saena giving birth to Kyoko, refuse to touch her, afraid to hurt her because she will most likely putting the blame in Kyoko when Saena is the one to blame for being an easy prey. Tsudou say he know about kyoko father 'what he thinks he knows' since he doesnt know his real name. It seem suspicious to me.
Do you think the dad's dead... After all she's claiming herself to be cursed...
but 'cursed' can mean so much >< but I don't think they had a fight and he left... maybe he got hurt and lost his memories of her... cliché...
Any Ideas? (￣ε￣)Σ