"They might think I'm a bad person, but nevertheless, I want to keep Ryou-kun all to myself."
Nagisa tries to use the deduction skill to understand the feeling. Cute!
Anyway, using the word "lover" sounds too mature, I think. In our language, "
pacar" is a gender-less pronoun for girlfriend/boyfriend. In another our language, there's also "
bojo" which means wife/husband, and is also gender-neutral. Both words are commonly used every day.
Well, that's probably one of the perks of the Austronesian language family, where gendered words are rare.