This is a heartbreak song that refuses to calm down. The singer opens by saying he simply cannot live "con esta triste condena" (with this sad sentence), and that there is no sadness sadder than "morirse de pena" (dying of grief). In Spanish, morirse de pena is an everyday idiom for being heartbroken, the way English speakers say they are dying inside.
The chorus is where he really lets go: "Esta maldita, maldita condena" (this damned, damned sentence) "que me anula y me ciega" (that cancels me out and blinds me). A condena is a prison sentence, so he is treating love for someone he cannot have like a punishment he is serving. My favourite line is "Me prohíbe inventarme contigo quimeras" (it forbids me from dreaming up fantasies with you). A quimera is an impossible dream, a lovely word to learn.
The verses are full of useful contrasts for a learner: "Unas veces pienso en el por qué, otras veces pienso en el después" (sometimes I think about the why, other times about the after). By the end he admits "Sé que voy a enloquecer" (I know I am going to go crazy). It is dramatic, a bit much, and that is exactly why it is so fun to sing along to.