Vagabundas is a beautiful and poetic word that literally means "vagrant" or "homeless". In this song, it's used to describe something as "wandering" or "fleeting".
The lyrics say, "...ilusiones vagabundas que se dejan alcanzar" (wandering illusions that let themselves be caught). This striking image describes a lover who chases after easy, shallow attractions instead of accepting the singer's deep, unconditional love.
This song is about a love that's completely one-sided. The singer feels an overwhelming, almost explosive passion, singing that their heart "estalla por tu amor" (explodes for your love). But the person they're singing to doesn't seem to care. They're so used to being adored that they can't see how special this is. The singer points this out directly: "Acostumbrado estás tanto al amor / Que no lo ves" (You're so used to love / That you don't see it).
While the singer offers something real and "incondicional" (unconditional), their love interest is out "jugando a enamorar" (playing at falling in love) with anyone who is easy to catch. The singer is left behind, hurt and crying. The song ends with a sad prediction: the person who hurt them will eventually just get lost in the singer's memories, a painful reminder of what happened.