Bethberry
First of all, this isn't what I wanted to say - unfortunately, its as close as I can come to saying what I want, so it will have to do, & I hope everyone can somehow pick up on what I really mean.
'Where' is Frodo? In his dream in Tom's house, he is, in a sense, both in his bed & on the ship, seeing the Undying Lands - his body is sleeping, but his mind is in a different place & time. Looked at in one way, he is always on Cerin Amroth, & always approaching the Undying Lands, always at every point in his story.
Memory is, as the Elves have it, a 'reliving' of the past, rather than a remembering of it. So, we are not speaking of looking back to something which is gone forever, but returning & being there, in full awareness.
Its like the book. We can open LotR & read of Frodo walking on Cerin Amroth whenever we choose, or read of him coming to Tol Eressea. Your quote takes that moment of him walking on Cerin Amroth out of the story & presents it to us, here, 'out of context'. So, in a sense, because the event has been described by Tolkien & set in print, Frodo is 'always' there, 'always' walking on Cerin Amroth. Aragorn never comes back to Cerin Amroth in the story, as a living man, yet he is 'always' there, with Arwen.
How shall we understand Arwen's 'return' to Cerin Amroth - as a bald statement of fact - she went back to Lorien? Should we not rather understand that she returned in spirit to that time with Aragorn, & only physically went to a deserted Lorien? When she dies physically, where is she spiritually? Still there, still with him?
I don't think we need to resort to ghosts returning to their old 'haunts'
Aragorn, Arwen, Frodo, all of them, are eternally in every moment of their 'story', & always will be.