In the first case of its kind in the country, the couple are seeking damages from their doctor after one of the women was implanted with two embryos instead of one as requested and subsequently gave birth to twin baby girls.
The women, who cannot be named, are suing prominent obstetrician Robert Armellin for more than 400,000 (330,000 US) to cover the cost of raising one of the non-identical children, who are now aged three.
The Supreme Court in Canberra heard that the couple's relationship suffered from the stress of twin parenthood and that the birth mother had changed after delivering the babies.
"She always said that she had a big heart filled with love," the woman's partner told the court, Australian Associated Press reported.
"I find (now) that she doesn't have the same ability to love that she used to and the same capacity to, I guess, embrace differences and issues as a couple or as a team."
The women also said that her partner had felt angry and desperate once she knew she was carrying twins and that she had hoped one embryo would just go away.
But Dr Armellin's barrister Kim Burke said the women's experience of losing their lives to the daily chores of looking after small children was commonly experienced by parents.
"You have described the situation nearly every couple in Australia suffers in the circumstances where they are no longer in a single relationship with each other but they've the burden of a child or children," Burke said.
The civil hearing is continuing.