The fact that he's sitting on the fence is a good sign that you're not driving him out. From what I've seen around the boards, he could sit on the fence for quite some time.
I guess it takes time for him to straighten out his feelings in his own head. But the longer he stays, the longer he has to get used to the idea of staying.
Even if he isn't conciously doing this, he's comfortable enough to stay put, and he'll just continue to get more and more comfortable.
