According to Marx, relations of mutual recognition (an idea of "love" that, as elaborated by Marx, appropriates Aristotle's idea of "friendship" ("philia")) would constitute the ethical content of a will autonomous in this sense.
So "association" in an ideal commonwealth would necessarily be fully "free"; such association would actualize the ethical content of fully free, "autonomous" willing and would provide individuals with what each needs to develop this autonomy.
Ted