You are allowed to not like people, nobody is entitled to being liked by anybody.
The MC is ALWAYS portrayed as keeping to himself and not wanting to interact with her, but she's the one who, 100% of the time, forces an interaction between them. The MC only acts in disgust an retorts to her behaviour when provoked, but he never goes out of his way to do anything that would hurt her feelings, it's always in response to her sexually harassing him.
If she likes being a slut more than the prim and proper person the MC fell in love with, that is fine, even by the MC's stance. He just doesn't want to interact with her, and there's nothing about it that justifies being called in asshole over!