Help! War movie / Something like a love triangle

I don’t remember much about the movie, but I do remember that it was about war and a spy girl. She had a relationship with two men but ended up falling in love with one of them.
And she wrote a letter to another man and said that she has always been in love with that one man
So she left that man
And in the night when it was snowing heavily, the girl went after the man she loved to save him

(I think the girl had long blonde hair
And the boy she fell in love with had a beard and was a military commander)