A Perth man living in a polyamorous relationship with identical twin sisters has spoken about the ups and downs of being 'the meat in the sandwich'.
Marc Glasby was married and faithful to his wife of 30 years, Belle; but then her long lost twin sister arrived on the scene and things got complicated.
Mr Glasby says he quickly fell in love with Dorothy when she and her sister were reunited three years ago, and they now live in a happy, healthy polyamorous relationship.
The sisters take turns sharing the bed with Marc, who admits there have been some turbulent times in their relationship.
Writing for News Ltd, Mr Glasby says sibling rivalry has reared its head over the course of the relationship.
"As the 'meat in the sandwich', as it were, I don't have jealousy issues to deal with, but my wife has had to work through these feelings and we have talked the issue over a great deal," he wrote.
"The relationship has not been without its hiccups, not least of all due to sibling rivalry that exists between sisters."
Mr Glasby believes his relationship with the sisters is a marriage in every sense except a legal one, and would like the right to marry just like any other consenting adults.
Polygamy is illegal in Australia, but there are no laws stopping consenting adults from living together in a relationship.
Polyamory is an accepted part of many cultures in Australia, including parts of the Aboriginal and Muslim communities.
But Christian lobby groups have seized on the perceived 'threat' of polygamous marriage to argue against the case for gay marriage in Australia.
They claim that gay lobby groups' arguments for equality in marriage, must also logically extend to polygamous marriage – a notion which has been rejected by lobby groups and The Greens.
Those groups say they are simply fighting for recognition of marriage as being between two consenting, loving adults, not a group of three or more.
Mr Glasby believes polygamy poses no threat to Australian society, and would simply legally recognise something which already exists here informally.
"I think in mainstream society there is a view that any kind of multiple partner relationship is all about sex," he wrote, "In our case, we really had no choice. The circumstances in all our lives were such that in order to move on, we had to be together.
"As I was already very much in love with my wife, and as I fell in love with her sister, and as the sisters had bonded so strongly after being apart for so long, our choice to live like this made sense."
The three partners will share their story, along with Aboriginal and Muslim partners living on polyamorous relationships tonight on Insight, SBS at 8.30.