If you love her and feel like this is going to eat you up inside then tell her. She deserves to know that she is married to a man who doesn't respect or unconditionally loves her. It is wrong for you to cheat on her and it is wrong (on so many levels) to cheat on her with her sister.
This is going to cut her like a knife! It is best to tell her now and sincerely ask for forgiveness. If she finds out later you won't get a chance of reconciliation.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.