ANSWER:
A guy does not need permission from anyone to get married to a girl. He is free to marry her if her wali agrees.
Do not ask about his parents sin as they are not sinful for rejecting you or about his sin for not trying harder! You are sinful for being in a haram relationship in the first place! You should be remorseful and asking Allah for forgiveness instead !
Cut off all contact with the guy and repent sincerely to Allah.