For eternity:
* E faavavau: This is the most common and literal translation for "forever" and means "for eternity."
For a very long time:
* E leva: This means "for a long time" and can be used to express a very long duration, though not necessarily eternity.
Always:
* I le taimi uma: This means "always" and implies a constant and continuous state.
For the rest of your life:
* I lou olaga atoa: This specifically means "for the rest of your life" and is used in contexts where "forever" implies a lifespan.
The best translation for "forever" will depend on the specific context in which you want to use it.