Alright- now if the answer is yes- then you should probably tell your friend, whether you think they'll like you back- or you just want them to know. I think they deserve to know. Who knows- maybe they like you too- and they are too afraid to tell you- in fear of what you may think. Its always best to be confident =D.
If the answer is no- you could tell them, but really- there's not much you can do.
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