Wow, you totally can't tell who likes and doesn't like Shuu in this thread. < <;;
Anyway, I think the forever thing can signal both his leaving, and his staying. Sometimes forever means that he'll leave, but they'll be rival's forever anyway, or, that he'll stay, and they'll be rival's forever anyway. It can work either way, and either way, what happens is what happens. One side will be good for one ship and the other good for another ship.
I personally think that Shuu is going to leave either way, and that's coming from a hopeful contestshipper, so you know. < <;; Besides, secondary characters never stay for long, and, if Shuu leaves, would Harley take his place as Haruka's rival? o O;; *shudder* That's a scary thought.