Red Dead Redemption Explained: What Does The Ending Really Mean?

John Marston met his wife when she was a prostitute. All the other members of the gang had sex with her. Still, he didn't care and proposed to her, because he saw something in her. Something beyond the exterior.

Furthermore, they have a child together and seem rather happy. He was able to separate her line of work from her as a person, which speaks volumes about the man that he is.

Miss Bonnie MacFarlane saves Marston when he's wounded at Fort Mercer, and there is clearly a connection between the two, but both don't allow themselves to cross that line, because Marston is faithful to his wife, and Bonnie is well aware of it.

When she sees Marston and his wife leave her ranch, she stands alone for a moment, contemplating what could have been. That's a really nice touch by the writers, showing that had the circumstances had been different, they would definitely be a pair.