so I like to do a mixture of Italian and English on this song. Here are the English lyrics (prone to differences in translations) and the Italian lyrics.

It's really a happy song, not a sad one. It's about saying goodbye to a life without a true love and going forward WITH this true love, to now explore things together. It's saying to goodbye to the life I had before you. That's where I sing it from. Hopeful and happy. :)
In English (generally):
When I’m alone
I dream on the horizon
and words fail;
yes, I know there is no light
in a room where the sun is absent,
if you are not with me, with me.
At the windows
show everyone my heart
which you set alight;
enclose within me
the light you
encountered on the street.

Time to say goodbye
to countries I never
saw and shared with you,
now, yes, I shall experience them.
I’ll go with you
on ships across seas
which, I know,
no, no, exist no longer.
It’s time to say goodbye…

In Italiano:
Quando sono solo
sogno all’orizzonte
e mancan le parole,
Si lo so che non c’è luce
in una stanza quando manca il sole,
Se non ci sei tu con me, con me

Su le finestre
mostra a tutti il mio cuore
che hai acceso,
chiudi dentro me
la luce che
hai incontrato per strada.

Time to say goodbye.
Paesi che non ho mai
veduto e vissuto con te,
adesso si li vivrò,
Con te partirò
su navi per mari
che, io lo so,
no, no, non esistono più.
It’s time to say goodbye