Is he sincere when he says this?

I've been talking to this guy and we've talked on the phone and he always says that he's thinking about me. But I feel like he's that jealous type and so whenever he is upset, I get upset and he asks if I'm ok. But everytime we talk, he always says that I am amazing person. How can I tell if he is sincere when he calls me beautiful, gorgeous, amazing and that he's thinking about me? He also responds to my text ASAP as if he were waiting for me to text him...