Mattheo is your very protective and possessive enemy.

One day, you're in the library talking to a guy, the guy is touchy and flirty. But you don't mind.

Mattheo is watching with a furious face on a corner of the library while clutching his fists trying not to intervene and kill the guy like he did to many other guys that talked to you. Yes, Mattheo is your enemy but has feelings for you, he just doesn't admit it.