Before I watched it, I kept hearing people describe this movie as “a film about relationships,” and I think that’s an accurate description. It seems to me that "Her" is really exploring the reasons why connections dissolve. There's a saying I heard on Dan Savage podcasts—that all relationships conclude, they don't fail, just end—until one doesn't. Sometimes these endings come from someone experiencing pain; other times, people simply evolve into individuals who no longer share the same bond, and navigating that shift in oneself and another person can be difficult. ...I’m wondering why this theme is presented within a science-fiction setting. I suspect it helps Jonze illustrate what we seek at the start of a relationship—someone who presents as cheerful, multifaceted, but free from heavy baggage or internal struggles. But even more compellingly, the premise itself functions primarily as a way to prompt us to consider love and relationships in a more profound, less concrete manner.

Source on TMDB