Definition of De facto partners
As per the Migration act 1958 (as per the latest amendments of 3rd September), a person is the de facto partner of another person (whether of the same sex or different sex) if, under subsection (2), the person is in a de facto relationship with the other person.
Definition of De facto relationship
The migration act has defined, a person is in a de facto relationship with another person if they are not in a married relationship with each other but:
(a) they have a mutual commitment to a shared life to the exclusion of all others; and
(b) the relationship between them is genuine and continuing; and
(i) live together; or
(ii) do not live separately and apart on a permanent basis; and
(d) they are not related by family.
There are some provisions that apply to the de facto relationship and partner. If you are after a professional advise in elated to Australian immigration, you can contact a registered migration agent to clarify your concerns.
Source – Migration Act 1958