I don't have any OST that made me cry, but if its okay, I'll post an AMV of Nostalgia. The song is A Thousand Years によって Christina Perri. This song really SUITS/スーツ their story. I cried so hard I was sobbing for the 次 couple of hours. ^^
XD Its because This アニメ is from the same 作者 of Junjou Romantica, so art is quite alike. This アニメ is Sekai Ichi Hatsukoi, its as amazing as Junjou Romantica! Do watch it! ^^