Prisionero means 'prisoner'. While it's a known word, its use in a romantic context is striking and less common than typical love song vocabulary.
In this song, the lyric "Y como un prisionero me llevas a tu cama" (And like a prisoner you take me to your bed) uses the word metaphorically. It conveys a sense of being completely captivated and willingly surrendered to the lover's power, making it a memorable and intriguing choice.
This song is a full-on declaration of love, so intense it's almost overwhelming. The singer feels he literally can't live without this person, saying he can't go on, "Vivir sin tú bella alma / Que me cura en un instante" (To live without your beautiful soul / That cures me in an instant). He sees his love as a work of art and feels completely powerless in their presence, admitting they are the one "que me mata con una mirada" (who kills me with a look) and leaves him speechless.
He describes a love that is both a sweet escape and a little frightening. It's a love that "me llevas a otro mundo" (takes me to another world) and takes away his pain. But he also confesses, "este amor es real, es lo que me asusta" (this love is real, that's what scares me), showing just how deep and serious his feelings are. He's ready to do anything for them, even cross the sea, because he wants to be with them "para siempre pa' la eternidad" (forever for eternity).