I feel like they're both saying this, but despite it being the same word, for Marisa it means "it suits me" and for Nitori it means "it suits you".

Nitori says “似合わねー”, means “it doesn’t suit ya.”

ordinary said:

Nitori says “似合わねー”, means “it doesn’t suit ya.”

I think I agree now that I've remembered how to inflect 似合う, and I still think they're both saying it.