Une vie à t'aimer is an argument, yes, and almost every other song references it in at least some small way, which means that at the end of Act 2 you come to realise that you have been hearing echoes of this in-some-way-familiar song, this well-worn argument, since the prologue, but only now at the end of Act 2 is the argument laid out for you in full. Everything that comes after is about explaining the finer points of it, gathering enough information to make a decision. The music echoes the writing; the music is in some ways far more explicit than the writing. The music tells you from the very beginning what the story is ultimately about.