Originally Posted by
Ouch!
If you want to, there are many little things that you can read into. Ashe and Balthier are among the only characters who interact privately about personal discussions (Balthier revealing that his father is Doctor Cid at Phon shore, for instance). In the background of some scenes when either Reddas or Al-Cid flirt with Ashe, you can see Balthier reacting with grimaces and annoyed looks, which some people might interpret as jealousy. Additionally, Ashe is the one shown to have the most emotional reaction when Balthier stays behind to save Fran. Balthier returning Ashe's wedding ring and Ashe crying at the reveal that Balthier is still alive also gets pointed out.
Aside from the canonical pairing of Vaan and Penelo, the Ashe/Balthier has more "evidence" than most other pairings, but at best it's a subplot, and never a fully-realized one. They bicker in a way vaguely reminiscent of how children tease each other when they like one another, and there's some pretty good evidence for at least a mutual attraction, but pushing much further than that is strictly in the realm of fan fiction, I think.