I like this girl and she kinda likes me but she has a boyfriend...what should i do?

her name is Sadie and my name Robert. she like me and i like her. but the problem is that she has a boyfriend. what should i do. because i told her how i fell but it was through a text message. i like her very mush and she kind digs. i know this b/c i see her some times looking at me well like staring and she Begins bit her lip and just like i don't know stares at me in till she receives text message from her boyfriend