Perhaps the other woman is his wife.
Damn, I'm 90% sure the other woman is the MC's wife. This is pretty messed up. I hope the MC gets a divorce before messing around with another woman so he's not as much of a piece of trash as his wife (since she's probably sleeping with someone else).
pg23 "el esposo de futaba-san", so the dvd was her husband cheating on her, why she's crying pg24/25
Definitely a twist, as it'd be typical for his wife to be on the dvd, maybe it is also his wife, but it seems like he didn't recognise her or the voice so probably not
Instead of making him vengeful or bitter, they aim to make him pity/console, even then though, his wife's been blowing the other guy, gay
Kinda funny this series hasn't been picked up in english, really don't care if it does, you only need to read a few words at most, so thanks Spanish translator for doing the work no one (naturally) wants to haha