I had the same problem and when I got back with him he did the same thing to me again. Then after that I decide not to ever do that again because it would be hard to change someone they have to do it there self. I don't believe it to be possible.
If he has said sorry and has not done it again/promised not to and you still cannot get over it then theres no hope. It is you're problem and if you cant deal with it, there is nothing he can do to fix it. The trust has been broken and is lost.
I have been in the same situation for quite some time and have realised that there is nothing my partner can do to fix what he initially did. These are the consequences; the relationship is ruined.
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.