My son is the twin of MyJoey's son - thank goodness we live in different states because the two of them together would be insanity.
If someone intermittently uses crack i think its only a matter of time before they become physically addicted. With polysubstance abuse i think they are addicted to the high - where ever that high may come from. At first they will do anything but eventually one drug will come around that will take presendence as the favorite or they will become physically addicted.
Crack is just not something you can do sporatically forever. Besides that crack is seriously detrimental to your health, illegal and the lifestyle of those he is getting it from and using with is extremely dangerous.