The law of marriage in Australia (which is non-religious)
does not allow for polygamous marriage (that is, more than one legal spouse at a time).
Although it is perfectly possible to legally marry in Australia using Islamic doctrine
(just as a legal marriage can be entered into using the doctrine of any other faith),
as a matter of law in Australia, only the first marriage "counts".
So if you are, and remain, married to him under Australian law,
then you are the legal wife.
It is not relevant that you are not currently living with him.*
As a matter of law, religious doctrine (of any faith) that allows for second and later wives
has no effect in Australia - they cannot be a "wife" in the way that you are.
Whatever the law in the country where he is, and regardless of religious doctrine,
so long as he is married to you, then so far as the law in Australia is concerned,
he cannot be in a valid marriage** with anyone else.
Likewise, religious doctrine is irrelevant to the law about how a marriage ends,
or what happens when it does (such as what happens to children and property).
In Australia, it is usual that the former husband and wife make an agreement
(often called a "settlement") as a result of ending a marriage.
Sometimes, they can do this privately. Sometimes, they need the help of the Family Court to do so.
There are people here better qualified than me to explain how that works.
But I do not see how an unrelated person, overseas, can have a sustainable claim.
I suggest that you seek the advice of a solicitor who works in the area of family law.
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Footnotes:
* Yes, separation is a proof of irretrievable breakdown of a marriage
(for divorce proceedings), but living in the same residence is not a proof of being (or still being) married.
** That said, it is possible to be still married to somebody, but be estranged
(often called "separated") from them, and be in an established (albeit de facto)
relationship with someone else). Such as man having a new girlfriend while separated from his wife.