*******SPOILER WARNING*********

Goodfella, the only way I can make sense of what Aspinu did is to think that he feared for his own life, because he had been extorting money from the group and putting it in Swiss bank accounts.
That seems like how Aspinu would act.

But if he hadn't tipped off the Don, Turi would have succeeded in assassinating him and Turi and Aspinu would have ruled Sicily.