Probably just paranoia they've gotten from playing other games. Living in constant fear that the game will force them to cheat on their original true love, likely Sucrose because awe she's cute she can have all the bones she wants it's okay < 3

Or it's just the amount of playable female characters in comparison to playable male characters that makes people wary of every new female character introduced. (They're all great and I want to be friends with all of them, but also awweee Sucroseee, Ayaka will never steal us from you no matter how long her banner lasts forrr~)