Is it possible to add one more character in your ring?
If yes, add a particle "no".
The particle gives you more choices, such as...
Eien(or Towa) No Ai 永遠の愛
Eien(or Towa) No Kizuna 永遠の絆
etc.
so far it looks like "Por Siempre Tuya - Forever Yours - (Japanese version)" I have max 40 letters available to me. That includes the lil hyphens too^_^;
I'm going to wait just a bit longer for more posts just incase someone might have something interesting. Thanks so far you all
Towa no ai (meaning "eternal love")
Towa no kizuna (eternal bond)
They're not exactly "forever yours" but is very natural Japanese in the same line of thinking. Plus, the two are very compact and smart. A literal translation of "forever yours" is not really "cool" in Japanese because it becomes too long. (Just my two cents... )