This is a love song from someone who never managed to say the one thing that mattered. The singer keeps circling back to it: "Lo que quiero decirte amor / Es que he sido tan feliz contigo" (What I want to tell you, love / Is that I've been so happy with you). It sounds simple, and that is the point. He writes "sólo pretextos" (only excuses) at night instead of the actual words.
There is a lot of honest self-blame here. "No por ti la culpa es mía" (It's not because of you, the fault is mine), he says, for pretending everything makes him laugh and blaming the rush or the cold. His real fear is blunt: going crazy if she left at dawn "sin haberte dicho" (without having told you). The dream images around it are lovely and a bit dizzy, like dreaming "que nos caemos" (that we're falling) or "que no amanece" (that the sun never comes up).
Learner tip: "he sido" is the present perfect of ser, "I have been". You hear it over and over, so it's an easy one to lock in. By the last line he wants "el mundo entero" (the whole world) and God to hear it.