Wife and I used to have a similar problem when we played MMO's together. We'd start characters and then play together awhile, then due to different schedules, one or the other would level up too far to really "run" together. So we'd start a new set of Alts to play together...
Wash, Rinse, Repeat until we had max characters :D
Now we tend to play Co-Op games instead like Lego.
@JayMonster: In FFXIV getting up to 50/60 is really just the start of the game, and the iLevel curve is pretty easy to catch up on so you aren't left behind easily.