Let's get this straight: Alduin saves your life.You kill a dragon.He's angry.You kill more dragons.You get ZA DRAGON SCROLL.When you start getting close he realizes you'll be killing him.He goes to kill you.You call a ole traitor of Alduin(Paartunax) and beat Alduin up.Then you track him down in Sovngarde and use the invincible souls there to kill him.And you kill him.The sad truth,because you'll be killing the dude who saved your life.