first of all, depending on your age. If you can leave and live in a home where morality is good, go for it. It is your way, big way, of letting your parent know, they are totally wrong and in adultery!
Speak up and tell your parent, you are in total disagreement and you feel bad enough to take a hike. You want nothing to do with the situation. If you are under age, that other person should not enter in your home. Your parent should be keeping you out of the situation. To take a gift, to give a smile, is giving them thoughts that you agree and accept the situation.
Don't be afraid at all to speak your mind! If you don't, and you want to speak your mind, you will feel regrets. It is best to speak up! And pray, pray, pray!