I am writing a story in which a young man (about 18) meets a 14-year-old girl, and they work together to overcome serious hardships. I mean actual, physical danger and violence, starvation, etc. A lot of the things they face are very difficult, and the girl is young and doesn't know all of the dangers they face at first. The male character is trying to make sure she survives, as he is in a better position to help her, and eventually they escape together. I haven't quite decided about that yet--as in, when and how they will escape, but I picture them having to walk a lot through woods and perhaps mountains, facing such obstacles as hunger, harsh weather, and the danger of being recaptured.
The story does eventually have them fall in love, and I suppose that would be natural considering all that they go through together. But they don't express their romantic interests in each other until much later on, when they are in a position to separate from each other.
The story is set in World War 2. The male character is a German officer of high rank who secretly renounces his office, and tries not to get involved in any cruelty.
My question is, how would the young man act towards the girl--how chivalrous can I have him be throughout all of this without making it seem too romantic? I want it to be somewhat romantic, but not sappy. Also, my character is already exceptional because of his refusing to go with the Nazis' agenda. How can I make him seem exceptional, but also not make him too perfect? I want him to be believable. These days, young men and women treat each other differently than back in the day. I am wondering what types of mannerisms would be natural for this kind of relationship back then, even if they would be considered romantic in this day and age.