Consider the concepts of 'free will' and 'imaginary obligation'. Under certain circumstances they seem hard to differentiate (i.e. somebody 'really wants' to relisten a track of music, or perhaps it 'feels necessary'). Under other circumstances they seem easier to seperate, but the difference seems closely related to subjective identification (i.e. on the street one person is asked by another to give his wallet, if he does so, is it out of 'free will' or out of 'imaginary obligation'? if someone sais the former you somewhat identify with the wallet-requester if the latter you somewhat identify with the wallet-donator, and the wording seems to carry connotation of either naivety, or insecurity).
The difference would be difficult to quantify from any point of view other than the individual acting. That is, the one choosing to do a thing, be it out of free will or imagined obligation. In the example given I would surmise that it is unlikely that the individual donating his wallet is doing so of free will. That said, it is impossible for me to know as an outsider. If I were the individual I may not even know what drives me to action.
A more common and direct example would be that between individuals and family members. In these cases however, the imagined obligation would often be so ingrained that the individual would think of it as free will. In fact free will its self has been subverted by conditioning during the individual's upbringing.
To bring this to an end, the difference between free will and imaginary obligation is a matter of source at best. At worst, it begs the question, "is there free will?" We will assume that free will exists, a broad assumption, for now. The source is what we should then discuss. What is the source or motivation of the individuals decision making process?
That is a simple statement but true none the less. If the individual fears something (anything) and that makes him decide on a course of action, it is from imaginary obligation. It is
The difference is categorical: "free will" is an ability, "imaginary obligation" is a motive.
Whether "free will" itself is real or illusory, person may feel obligated to do A, but is still free (or at least feels as if free) to act out or ignore the obligation. The (imaginary) obligation then counts as one of perhaps several reasons in favor of choosing A over B (C, D, ...).
Person may in fact have/imagine multiple conflicting obligations and need to exercise his/her (illusion of) free will to choose which one to satisfy.