How to know if your crush just admire you or is really interested in you?

He is a flirty guy,there is a time during class he was staring at me and says that i am pretty he say that not only once but many times.what does it shows?And last year i went to visit one of a school and a guy ask for my contact number. And my crush was like saying got guy ask you for contact number...But i ignore him. Then i overheard that he said ''today is my worse day!And after that about a few day past he was like asking for my contact number but i did not give him.He ask for my friend for it,and i receive a msg i don't know who it was at first the sender write to me who you like now?then i was puzzled who it was then he said that he was that guy from the school.So i know that he was lying and i found out it was my crush why did he want to lie?