Praise be to Allaah.
You must repent to Allaah for what you have done and stop whatever haraam deed you are doing, whether it is major or minor. If you feel that in order to stop doing this haraam deed you have to marry this woman even if your parents do not agree, then go ahead and marry her, because that is the lesser of two evils, and try to please them in other ways as much as you can. See Question #988, 1114 and 1805. We ask Allaah to protect us and you from committing haraam deeds.