Is it too good to be true? - yup, the perfect, unsuspecting affair. If you're into that. Perverts? - Sort of. To break down the mental barrier that you are related would mean you both really only have one thing on your minds, be it sex. Psychological help? - Well I don't fuck my sister, so maybe. I don't agree with incest, sorry.
you should get your mom into the scrum and have some REAL fun.... hey maybe your son will start fucking your daughter..but that would be fine with you because you are no hypocrite
If I leave aside the judgment of incest, I have two questions for you. How many people are going to be hurt by this when it all stops being a secret that you think you can maintain? How many in your families and circle of people are going to be accepting of this? If you can answer, no one that matters or that it does not matter to you, then continue. If you can not answer that, then maybe you have an answer. Perhaps instead you and your sister have far larger issues to work out with your own lives and families.