I know that when Lily sacrificed herself for Harry, Voldemort could no longer touch him and any attempted Avada Kedavra on Harry by Voldemort would rebound onto himself, until, of course, he took some of Harry's blood and put it into himself.
Now Harry and Voldemort share Lily's sacrifice and protection and also share Voldemort's soul since Harry is a Horcrux. When Voldemort tried to kill Harry in the Forbidden Forest, Harry was kept alive by his own blood which ran through Voldemort's veins. When Harry then challenged him a second time, Voldemort's killing curse rebounded onto him yet again since the Elder Wand won't kill its master.
But Voldemort shouldn't have been able to die since Lily's blood sacrifice lived in him and Harry should never be able to die either... shouldn't they both be immortal? I don't get it, someone help!