Actually, this song reminds me a lot of Vaan and Penelo. Pre-game he was always running off and she'd be left worrying about him. And even though he still goes off adventuring, he probably settles down with her a bit.

I think the song is supposed to have a broader theme of exploration and moving on, something that Ashe experiences throughout the game. But I don't think she and Balthier really have anything that rivals him and Fran. The game makes it quite clear she's not over Rassler; I view death as another form of exploration, so this very well could be about Ashe and her departed husband.
huh........that actually makes a lot of sense to me =o! I never really thought about any of that....thank you very much xD