Hi Bob, how about chatting to him or rather both of them and be honest with him. Ask what their expectations are for the future. Then see how you can all help each other, you need them as much as they need you at the moment.
If the guy has aspirations to earn more money don't knock it, help him and yourself at the same time. He could certainly use your experience if he's looking to setup a round of his own, I would suggest that you see if he would like to manage some of the customers on his own or rather new customers that "he" brings to the round.
Grow the new business together whilst retaining your own round, take a small percentage of the money from the new customers he brings in but work with the guy. If he buggers off with a new bird and a new idea, you have extra customers to pick up :-)
Don't forget to look after the other bloke though, if he's picking up his mates work on your old round then reward him for the extra effort, it's a good lesson in life for the three of you
