Responses

he was pretending, he wanted cirrus and his step mom to be a family, hence why they pretended to be close whenever he was around. this is further elborated on when we see young cirrus crying because his mom died, cirrus' dad got tired of hearing it so he "replaced" cirrus' mom with step moms. he nice to cirrus in the beginning because cirrus was being "perfect" pretending to like his step mom, no longer causing problems at school, etc. we see him change as cirrus decides to cause more trouble, revealing how he truly feels towards cirrus.
why did cirrus' father got a complete character change? wasnt he lovey dovey with cirrus in an earlier ch?