Hmm... I don't like the lil' sis who said she makes Elsa feels better than me. Is there a possibility to enter in a war with Mia for settle things like that ? If Mia takes to much liberty, the relation with the MC will not remain good. Time to tell her some things to calm her down.
Maybe something like :
" Ok, why did you tell Elsa you'd make her fell better than me ? Making fun of me ? It's not because you were the first have fun with her that you can said that ! "
" Hu?! I am sorry, I didn't want... "
" I am angry at you sis ! And why you didn't tell me you had fun with her in your classerom ! You want me not fuck you anymore ? Don't do that again before you tell me ! "
Or something like that...
The game need some choice like the one with the psychologist when she kiss the mom and the MC was not here. If the girls have fun without you and left you out, that will be a problem...