Desmejorada means 'deteriorated' or 'looking worse for wear'. It's an interesting word because it describes a state of decline, often in appearance or health.
In the song, the lyric
Nelson Arrieta and Ronald Borjas bring us a beautiful declaration of love in "Lo Eres Todo (En Vivo)"! This song is all about appreciating that special person who is everything to you, even if you don't always say it perfectly.
The singers admit they aren't perfect, singing, "yo sé que no soy perfecto que no te digo a todo momento que te amo tanto" [I know I'm not perfect, that I don't tell you all the time that I love you so much]. But they make it clear that this person is their "fuerza" [strength], the "beso que me das cuando despiertas" [kiss you give me when you wake up], and even the one who "me lleva a hablar de Dios" [leads me to talk about God]. It's a sweet reminder that actions and deep feelings often speak louder than words, and that true love is about being each other's reason for living.