Hi Oikos,
I never answer to the people who registers to ask for a translation and not to try to do his own translation, specially I don't answer to the people who registers the same day that asks for the translation; but this time I will do an exception.
This is the Spanish translation for your poem, it has also rhyme in Spanish, there is some change of word in order that the rhyme was possible. I hope that your gf doesn't erase you of her heart.
ESCRIBÍ TU NOMBRE EN EL CIELO
PERO EL VIENTO SE LO LLEVÓ
ESCRIBÍ TU NOMBRE EN LA PLAYA
PERO EL MAR LO BORRÓ
ESCRIBÍ TU NOMBRE EN MI CORAZÓN
Y PARA SIEMPRE EN EL SE QUEDÓ.
Regards.