Les Miserables teaches how grace and forgiveness can be applied to our own relationships.
It is what it is, and you choose to release the perpetrator of the responsibility of restitution. There is no thriving marriage that has not had to forgive major and minor things. There is no long-term loving relationship that has not endured the pain of being known as we fully are, nastiness and all.
In the words of Victor Hugo himself, the author of Les Miserables:
"So long as there shall exist, by reason of law and custom, a social condemnation, which, in the face of civilization, artificially creates hells on earth, and complicates a destiny that is divine, with human fatality; so long as the three problems of the age — the degradation of man by poverty, the ruin of women by starvation, and the dwarfing of childhood by physical and spiritual night — are not solved; so long as, in certain regions, social asphyxia shall be possible; in other words, and from a yet more extended point of view, so long as ignorance and misery remain on earth, books like this cannot be useless."
In conclusion, the lesson learned from Les Miserables was: Everyday is a new opportunity to courageously accept forgiveness and to live according to the grace I have been shown by God and by so many.