don't tell them or let them figure out
keep it to yourself, especialy if you know who he/she is in love with or if you know you don't have much of a chance
because it will turn out to be just plain awkward and everything would change from that moment, you can't tell your friend you love her and she doesn't and then the next day hang out in the cafeteria as if nothing has happened
as you can see I gave it alot of thought, I think I am begining to fall for my best friend
though I've known her for about 2 years now, I wonder what's with the late feelings all of a sudden