Stubborn to the point that literally every time she sees him she tries to force him to open up to her. That sounds a bit obsessed to me.
That's honestly a good question.
She says he's the best looking guy here and pretends to cast a spell on him saying "You're-going-to-like-me" how is that not flirting? Let's not forget her first reaction to seeing him on the train mission is to run up and hug him.
Wouldn't that just make him even more afraid of getting close to someone? Especially how Quistis and (to a lesser extent) Selphie both tried to get close to him before he met Rinoa, and he brushed them off like nothing. And he shows no signs of being infatuated with Rinoa when he next saw her, not even in his inner thoughts.