Harry Potter: The creature Queen

when Harry saw his godfather begin killed and throw into the veil of Death something snaped in him. Not to mention when dumbredore told him the proprecy he knew something is wrong since dumbredore is very powerfull why can't he just kill Vordemort after all he sure could.

PS:I get that idea from WinterWolf-99 Harry Potter: Heart of a Mystic soul or Harry Potter: Adopted by Roses