I can only guess at how confused you must feel about what you have discovered, Patagonia has raised some of the many questions which I'm sure are already spinning around in your head. But although I can understand that you probably feel like you need more information, I can also understand that this guy would probably prefer not to discuss intimate details of his incestuous indiscretion. If fact most people would not want to discuss their previous relationships and would be annoyed if their new partner insisted on knowing every detail.

So I guess what you should do is make your decision on whether to continue with your relationship on things like has he given you any reason to believe that you can not trust him ? To the best of your knowledge is he honest with you ? And can you get over your jealousy or is it something that is always going to be a sticking point for you ?

Finally just one more thing..... I have heard about such intimate relationships happening with family members that have been estranged until adulthood. I believe the reason supposedly behind it is that when family members come back together there can be strong loving feelings and almost an instant chemistry but it can be hard to rationalize these feelings and they are misinterpreted as sexual chemistry. Might be worth doing a little research it may give you the answers you desire

Good luck