its weird, but i exactly wanted her to cheat on Chad to
win over Chad. and it makes her not enough good for any relationship.
so
she gave me what i wanted -> not good
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if she wouldnt gave me what i wanted -> bad
she has a situation where she cant win, cant be good.
as i recall, Sage and Chad are toughter for 2 year at least. Sage probably as any other girl, want bf from near 15(?) years old times. if Sage is 23, that mean 2 out of 8 is 25% of her "love time". i give her, its pretty deep. i cant recall any dialog about she had other bf, so maybe he is her first relationship. and maybe for sexaully too (she had not threesome too, so why not). that makes it more deep for her. plus, Chad cheat on him, takes her as nothing as you said. so, Chad makes a feeling in Sage, she will lose him. peoples dont like losing for sure. (Chad deny the cheating at first)
Quinn bought lessons and other things from Sally. after Sally is clever, this lie fit very well. probably Karen, the another nerd has good grades too. if there was others, than probably Quinn tell something false to Sage. Later Sage just accept the fact, Quinn is very popular.
Quinn and Rio started fought in the game. Rio say to Cammy they were "=" /partners in the past, and Quinn wasnt her boss. so, maybe it was only at few times. maybe they were just lucky. but honestly, if i hear two woman's fight, but dont understand the words, i wont think they had an illegal restaurant + magic mushroom and magic dust shop. + Sage trust in Quinn, so lower chance for eavesdropping.
ps: mc is retarded, the story and other parts why not?