Michiru's parents are still Shiou's dad Hawaii mom. Shiou's dad is part lion, part wildcat. It was a 50/50 chance of Shiou and Michiru being lion or wildcat.
No one cheated on anyone. Michiru's mom told him about his dad and even said "he didn't even tell you?"
http://www.mangago.zone/read-manga/nekoka_danshi_no_shitsukekata/mh/v05/c025/pg-21/
It really was ridiculous that the dad didn't tell him lol, all that drama for nothing!
Ikr!
But suddenly the ending just collapsed.. Like Mangaka forget or couldn't figure out fully where to go with the story and just rapped it up fast. Maybe it didn't get more volumes so mangaka had to just tie up the ending somehow and it fall apart?
There was many thing what I never quite understanded.. So Hawaii mother wasn't real mother and real mother cheated Michiru's dad or something? Who are Michiru's real parents? Like WTF?