if that person is a friend i try to forget, my crush and find something else to do instead of ruining a really good friendship, i've had to do this a couple of times
a side note to my post above: i kissed my second best friend once at a party or rather he kissed me, he said it was a good night kiss but ehm.. he tried to stick his tongue into my mouth, both of us were drunk though, two hours later i walked up to the living room sat on the couch met my best friend again he was by then seriously wasted, he said he wanted to sleep so i said he could use my shoulder, but his head ended up in my lap, i told him to just try and sleep, then his hands went up to my thighs and i told him to stop he did'nt stop so i slapped him on the hands and told him again to stop then i slapped three times straight on his face and i said "stop it it's not right, i swear if you don't stop i'll scream" lucky for me he stopped after he heard my tone, and a female friend of mine showed up.
ok don't take this wrong i liked that he kissed me and that he touched me but it felt so wrong at the same it felt right.
treat them well... and dont act like you love them... they might never love you so try to get over it i guess... its happened to me 3 times before... the feeling wont last forever.