When Kurt was 12/13 he was raped by his piano teacher. After that he was getting really sick so Burt took him to the doctor. Turns out that Kurt is pregnant, Burt blows up at him because he is like 12, Kurt tells him that his piano teacher raped him. Burt feels some angst because Kurt wanted to quit the lessons but Burt wanted him to continue.
Kurt is considered the class slut in high school. After he joins glee he is sitting in the back of the class(?) with his headphones on and the people are talking about him (Artie for sure). Kurt goes all "why don't you just ask me?"
Also Puck is a transfer student and really likes Kurt, he is the first person to meet Kassie (i think that's her name) and she calls him Uck.
Oh one day there is this competition in glee and Kurt has to bring Kassie because Burt cant watch her. Matt and Mike (?) sing "The Bitch Of Living" fro spring awakening and Kurt is in totally daddy mode ("Kassie don't repeat these words, okay?"). Kurt and Puck win and Kassie announces it for Mr. Schue.
Another thing: Brad gets sick or something and glee needs a replacement so the school hires Kurt's old piano teacher. Kurt doesn't want to go to school but Puck and the rest of glee rally for him and his piano teacher goes away.
Kurt and Puck fall in love and eventually have another kid.
I hope this is enough info. thanks!