It was easy enough, early on, to keep their world spinning as he liked. Some subtle encouragement of Tamaki's wilder ideas, a touch of sympathy for Haruhi's plight, and everyone was swept along nicely to the natural conclusion: Haruhi's debt increased and Tamaki apologetic and eager to do better next time.
It worked well to keep them both in his orbit.
Now, as graduation looms and the red in Haruhi's account dwindles, he knows those days are reaching their end.
It's not in him anymore to simply let things happen as they will. He'll have to think of something else.