Warning: Readers who haven't seen Before Sunrise, Before Sunset, or Before Midnight will encounter plot spoilers below.
"We know that we are going to break up eventually."
So says a young woman in the middle of her first great romantic attachment. The context is a dinner with cross-generational acquaintances at a villa in Greece. Three couples of varying ages are discussing friendship, companionship, commitment, sex—all the things that pass for or indicate love in the modern world—and they all seemingly agree on one thing: nothing relational in this world is permanent. Or if they don't agree, nobody is willing to fly publicly in the face of what has graduated from conventional wisdom to accepted fact.
Men and women want to love and be loved. They want it desperately enough that they must and will keep pairing off, even as they loudly and persistently declare that love's attainment is at best a random, lucky draw, and at worst—and most probably—a fairy tale.
I have always thought it significant that when Celine (Delpy) and Jesse (Hawke) met as strangers on a train eighteen years ago (in Before Sunrise), the reason they first spoke with one another was in shared disgust at a publicly bickering (apparently) married couple. There follows an awkward, recycled joke about how married couples lose the ability to hear the pitch in which the opposite gendered partner speaks ("nature's way of allowing couples to grow old without killing each other"). Jesse later shares that his parents once said they stayed together only for the sake of the kids.
Message to Boomers, Gen-X-ers, Gen-Y-ers, and Milennials received: there's marriage and then there's love, and never the twain shall meet.
Dismissing marriage and searching for what could possibly replace it to signal that a relationship is special—nay, unique—ties the three very different Celine and Jesse movies together. In Before Sunrise, the characters speak in emotive, modern spiritual language (they have a "connection") to persuade themselves and others that they're being driven toward intimacy by something other than emotional infatuation or physical desire.
But they can't solve the big problem: how to demonstrate that claim in action, how to differentiate this relationship from a hook up. Celine's one idea is to refrain from having sex, since that will at least make their relationship different, even if she assumes it will still only be a one-night affair. They don't follow through (though this isn't confirmed until Before Sunset), but they do manage to not exchange addresses or contact information so that the planned meeting in six months can be entirely voluntary. Even this seems more like they're rejecting any external, concrete obligation than attempting to forge their own kind of covenant. They see commitment—even just a commitment to call, write, or see each other again—as a form of bondage, a poison to a love relationship, despite the mutual assurances that continuing the relationship is what they both want.