My protagonist has a deep, complex dilemma I have trouble portraying. Basically he hates Nazis, but is forced to work for them and become one. He also falls in love with a Nazi girl. How could I portray the dilemma of being treated nicely by the nazis (some of whom he genuinely likes) and resenting them?
I agree with Aaron DC, in addition, you could approach this through different mediums too such as diary entries or possibly writing in past tense like he is reflecting on the events
I think you should give the reader the same dilemma. Just show the Nazis he interacts with being nice to him and each other. Put your MC in their debt by having them act selflessly to help him. Show them as people with friends and family that they love and would do anything for. Then have your character see the devastating effects the Nazis are having on Jewish people and the other people they are persecuting. Show them acting cruelly and completely inhumanely to people they view as substandard. Show that the Nazi girl, if you want her to be a sympathetic character, truly believes that what she's doing is right, even though it's obvious to the reader that it's completely wrong. After that we are going to have the same problem of trying to reconcile their kindness with their evilness. We don't need a whole load of monologues from your MC to know the struggle he's going through.
A dilemma is where someone genuinely doesn't know which of two options is the correct one. In a story, as in reality, people often don't have full knowledge of what's going on. Everyone is ignorant of a great many things. I'd play on this. Why does the MC hate the Nazis? Perhaps he's been brought up to do so, but when he comes to actually know some of them he discovered that they're not the monsters he'd always imagined. The MC hears about the Nazi's aspirations for national development and thinks them good and noble. What he sees in the way of law enforcement, he thinks of as heavy handed but probably necessary, being unfamiliar with that kind of task. He knows for a fact that stories about the Germans that were circulated during the first world war, were a pack of lies. Could the rumors he's hearing be such propaganda? He can't be sure.
Really good advice, all of you! It's helped me greatly in portraying everyone as more three-dimensional characters on the whole.
The most important thing to remember is not to write about the Nazis with the advantage of hindsight. Most of the German people of the time trusted and believed in their government, and like anywhere, most of them were normal, decent people. It is remarkably hard to hate an entire nation of people once you see them as mother and father, children and old folk, as real people and not just cartoon monsters.