this is a genuine instance of the topic being subject to the "interpretation" of the viewer because there is no other dialogue.
michael had to say goodbye to his brother by blood, bug, and now was having to part ways with the last remnant of his childhood, duquan.
duquan desperately went through every far fetched scenario to stay together, but michael knew this was the end and goodbye.
I thought he hesitated and looked download at the disappointment of knowing that Dukie has become a drug addict. And that Dukie was doing what crackheads do; Trying to get old friends talking so they can hit them up for cash....In my mind, I think Michael now knows for 100% certain that his only friend left in the game is now a mark and he no longer wants any part of dealing with him because he knows marks will either get him arrested or get him killed. Michael was thinking a few steps ahead while the book smart Dukie was now thinking a few steps behind
or he could have just forgotten. After all he is grown now