I think the love story was between Vaan and Penelo and Fan and Balthier. On one of the viera sidequests, a man mentions that he would've never considered falling for a viera if he hadn't seen Balthier and his partner, who is obviously Fran. Then, on another sidequest, a Viera takes an interest in Vaan, then later says that he already has someone who loves him very much. Hmm.. I wonder who that could be? 


, and even though you guys are repulsing at the thought of Ashe and Basch, think about Fran and Balthier because on viera's longetivity Fran is over 50 years old and Balthier is 22
not that I care, just making a point.
but yeah Balthier and Fran are good as a couple 
, and in FFXII, since Vaan is not completely linked to the goings-on, and you can play as anyone being the 'leader', they wouldn't throw in a love scene between Vaan and Ashe/Penelo, because if you were playing with a completely different team, it could be kind of random? I don't know if I worded that right but that's along what i'm thinking xD