How to optimize the next years of PhD
If your professor really doesn't want you to leave, he needs to offer you a permanent position. It may be that keeping your association going would be good for you. But you need to leave the nest eventually and fly on your own. 

But it sounds like you are in a good position to finish your doctorate early. I suggest that you do that, at least. Accelerate anywhere you can. 

There is no reason that you can't explore a position elsewhere as you get closer to the end, to see what is on offer. It is good to have options. 

To maximize your future, stay as helpful and cooperative as possible.