Do i have an obligation to say something to this girl?

[sevs]

theres a girl that likes me in my marketing class supposedly …her friend just gave me her facebook…ive actually kind of known for like a month and a half now cause her friends on the track team know me and they told me she stares at me or something…but I just haven’t cared and I feel kind of bad. plus theres a girl that ive known for couple years online and these last few months weve really started liking eachother and i think that may have something to do with it...should i try to pursue real life options over an online relationship even though i dont really care about this girl in real life? do i have an obligation to say something to her (even if i would just be saying lets be friends after hanging out or something) or just keep ignoring her?
Shes in my major so I am going to probably see her around and I dont want it to be akward....

[me]

You don't have any obligation to this girl and the more you get involved with her/talk to her would probably be worse if you aren't interested in her and she likes you.