Cant stop thinking of her?

theres this girl that i really like and i dont know if she likes me. i took her to prom and we had a good time. im really shy and i dont have her phone number. i talk to her online but the convos are usually short because shes not on often and is away most of the time. i always have to im her first to start a conversation. if she never ims me first does that mean she isnt interested in me or am i thinking too much into it and should keep talking to her? should i maybe im her less so she doesnt become annoyed? i took her to senior prom and i went to her dance recital she seemed happy to see me...she comes into my work once in awhile and says hi to me everytime ( that could be just to be nice). My friends girlfriend knows her and was going to ask her what she thought of me... should i ask her what she said about me before i stress out about it?