What does it mean to say "I love you"? And how do these three little words change our sense of ourselves, our commitments, and our future?
Imagine you've been dating somebody for a while. Things are going well. You like each other, and the dates are all enjoyable and fun. You are pretty happy with how things are progressing. But one day, the other person turns to you—an intense look on their face—and says in a tremulous voice, “I love you.”
You are stunned. Astonished. This puts things on a different footing. Everything has moved up a notch, and you are not sure how to respond. Perhaps your reaction to this revelation of love is pleasure and delight. Perhaps you are horrified, and you descend into wild panic, making your excuses and resolving to cut all contact. Either way, this declaration of love has changed things. There's no way back from saying “I love you.”
But this is also pretty strange. What has just happened? Why has this declaration—these “three little words” as the popular songs have it—had such a transformative impact? One answer is given by the philosopher Alain Badiou, who writes that:
A declaration of the "I love you" kind seals the act of the encounter, is central and constitutes a commitment. 
For Badiou, love always begins in contingency, in chance encounters. But with the declaration of love, something changes. Saying "I love you", Badiou writes, is a way of "locking in chance" . Until now, this love affair has been another uncertain, changeable thing in a world governed by chance. But now this declaration has been made, something new has entered into the equation. What was once under the spell of chance now becomes an opportunity of constructing something new: a new truth or a new future. Again, Badiou writes that
But chance, at a given moment, must be curbed. It must turn into a process that can last. This is a very difficult, almost metaphysical problem: how can what is pure chance at the outset become the fulcrum for a construction of truth? 
No wonder it's such a big deal when somebody says, "I love you." Because perhaps this simple statement is, as Badiou concludes, "a declaration of eternity to be fulfilled or unfurled as best it can be within time: eternity descending into time."