My wife and I taught engaged couples in church approved pre marriage retreats and the concept of God being present in the couple and family relationship was a key concept. Each partner should reflect God’s unconditional love to the other. It is the closest that any of us will get to that love and forgiveness. God is present at all times and even in the creation of new life. You are mistaken that this is not Christian marriage theology.
AS a Christian trying to show my love as being equivalent to God’s love is an ideal. It may even be the best way to stay married. That is not what Les Mis is talking about nor is that the message of the movie. You have neither read the book nor seen the movie. You comment does not even come close to addressing the actual content and meaning of the movie.
I am glad you do work with couples in pre marital counseling. That is a good thing. I do believe that if more couples had the idea that today I am going to do things to show my partner the love that God has shown me then more marriages would last. That has nothing to do with this movie