The saddest part is when Savannah finally told John about everything. The reason why she married another man when John was away for war.
"You think it was tough out there? Think it was easy for me without you? You thought that every single day wasn't a goddamn marathon of my life without you? I was alone and I had no idea what I was doing."
She tried her best to make the situation better for the sake of the family, for the sake of the little boy to be exact. She married the man thinking she could actually help him to raise the boy. It wasn't that easy as John was not there with her.
Maybe it's true. When we're struggling with something, it is best to see the people around us. We should realize that everyone is struggling too as to them it's just as hard as what we're going through.
p/s I watched this movie long time ago and I barely remember the real plot. It's just that I found some pictures of the movie in Twitter and thought of something : One has to sacrifice.