How do you know if you have feelings for someone or it is just that you are surprised by a guy not being an asshole?

And I'm not used to having guy friends around my age because I've never had that many of them before. And I don't know how to react to people that just accept you for you. Especially guys. And I've hardly ever spent any one on one time with guys around my age. Even just as friends. I don't know how that's supposed to feel. Especially since I feel so deeply and care so deeply for so many people already m.