I agree that in most cases determining if a de facto exists should be fairly straight forward... HOWEVER, in determining if a de facto exists for the purposes of family law it can become a bit more complex.... Section 4AA of the act that defines it, whilst saying that a couple must be living together in a genuine domestic relationship, doesn't say that a couple has to be living together full time.... There are cases where a de facto has been determined to exist where the couple were not living together full time, but when they were living together, it was a domestic type relationship, ie, they shared a bed, meals, outings, etc.....Okay - Regardless of which law we're talking about, one common element that is required to be classified as a defacto is that you must be "living together as a couple". So the first thing that needs to be established is whether or not you are actually living together. Only then can the question of a defacto relationship be looked at.
That said, I think in this case, the OP has nothing to worry about as long as they don't have a child or jointly contribute to the acquisition of major assets