Quimeras refers to fantasies, illusions, or dreams that are difficult or impossible to achieve. In the song, "la vida se aleja y nos deja llorando quimeras" means that life moves on, leaving us mourning the possibilities that never came true, making this a poetic and memorable word.
"Amar y Vivir" is an old Mexican bolero, sung here live in Mexico City by La Santa Cecilia with Comisario Pantera. The first verses ask why this love should stay hidden: "Por qué no han de saber que te amo vida mía" (Why shouldn't they know that I love you, my darling). The singer would rather be seen crying one day than keep quiet, and if anyone asks, "Diré que te quiero mucho todavía" (I'll say I still love you so much).
The chorus makes the case for saying it out loud: "Se vive solamente una vez" (You only live once), so "Hay que aprender a querer y a vivir" (You've got to learn to love and to live). Life "se aleja y nos deja llorando quimeras" (drifts away and leaves us crying over pipe dreams), and the singer refuses to end up regretting "lo que pudo haber sido y no fue" (what could have been and wasn't). The last line is the promise: to enjoy this life with the other person close "hasta que muera" (until I die).