I would like to remind everyone that they were already in love with each other and in a relationship before they knew they were related. The professor already got kicked out a long time ago and the Dragon family doesn't care about him, the woman has been in essentially seclusion w/o caring of the Dragon family as well. At that point, semi-incest be damned if they both can't forget each other for 20years and both are completely miserable, how much worse could it get. Even if this were real life and the same scenario played out, I would be okay with it as their circumstances are so extreme.