As Damon gains humanity, Stefan... loses. And I'm guessing he loses not only his fancy 'vegetarian vampire' status, but also his place by Elena's. Anyone want to audition for the role of Elena's sidekick? Too bad, Damon's won it.
Stefan may get a taste of human blood again soon, which may change his personality a bit, and I can't imagine that goes over well with good girl Elena. Katherine, on the other hand, would love it, right?
There's definitely a Damon/Stefan switcheroo thing going on here. Are you up for this wild ride or prefer your Salvatore brothers The Way They Were?