when I'm at his house.. I secretly copied all his files. (pls don't tell any1 about what I did)

so now I need some1 to finish this song!! I've bEEN DYING TO PLAY THIS SONG!!!!

No clue what you're talking about, but I think it would help if you provided the name to that piece, since I've listened through the OST before and don't recognize which piece that is.

http://www.youtube.com/watch?v=BA5r867qV3s

or here
http://shiroikumo.imeem.com/playlist/ljf_zB54/fate_stay_night_ost_music_playlist/

the name of the song is Kimi to no Ashita or something