Through out the book draco has seemed to be a character sworn on making Harrys life a living hell. Dumbledor seemed to almost be like a second father to Harry a person who looked after him and tried to lead him in the path of love and friednship adn to bbe good. Buth dumbledore had secrets of his past that no one knew abou that made harry somewhat thinking that maybe dumbledore shouldn't have been Trusted and Draco was never to be trusted.
Throughout the book both of thes charatcers took a ride with Harry on everyone of his adventures wether to help him or to make sure he failed adn although repeatingly he almsoted failed and through sometihng he manged to succeed. Dumbledore was harrys closest thing to a reall father or a very good friend before siruous. Draco was the absolute most evil thing in hogwarts to Harry and he thought that would never change. Whne dumbledore died that was a turning point in harry's mind saying that he must now take hold of his future and figure out what to do with it because before that he was just trying to survive school and he had dumbledor to help take care of him and keep him safe.Without dumbledore he felt as though he had no one to keep him safe or lead him to safety. No one to protect him anymore.
With draco being slowly led into believing the dark lord is right that Harry should die that theres no other rule but lord voldermorts. He just had to roll with the punches and forced to feel as though he must be something he is not hes forced to be his parents image of the perfect son and voldermorts perfect piece.
In my mind i see this game as a chess gmmae and all the important people are the pieces adn since Harry was little it was dumbledore and voldermort playing the game. But when dumbledore died voldermort believed he won but didnt realize harry was being tain to win the game and not to lose adn it led out to he had to fight this battle on his own whilst voldermort didnt care who he sacrificed as long as he won.