HE'S the person she turns to when she needs a lift home from the airport, career advice or a shoulder to cry on.
Since meeting at a book club four years ago, Melbourne residents Claudia Bergsdorf and Christian Moura have gone to countless plays and concerts together, as well as shopping for furniture and exchanging thoughtful gifts.
They are currently planning a holiday for their annual joint birthday celebrations, and used to share a whisky to unwind until a health condition forced Claudia to stop drinking a couple of years ago. They message constantly on WhatsApp and try to see each other at least every second week.
But Christian isn't Claudia's husband or even her boyfriend, though he is her next of kin.
And she isn't the only "wife" in his life.
"He is a bit of a husband to many women," said the 33-year-old graphic designer, who is a dual Australian-German citizen.
"There's maybe four or five of us 'wives'. I am probably the closest to Christian at the moment, because his other 'wife' Lydia had to go back to the United States. If she was here, I'd say that she is Wife Number One - but by default, I am now," she added with a laugh.
Christian's life sounds busy enough as a 'part-time husband' to a gaggle of women - yet he also has a long-term, live-in girlfriend.
Surely she isn't comfortable sharing him?
Jen Ross admits that she was somewhat wary at the start of their now two-year relationship.
"At the beginning, I felt a little bit of uncertainty," she said. "That came from my past experiences in relationships and having seen other guys with close female friends and it not being completely platonic. But I relaxed into it when I saw how Christian is with his friends."
However, Jen added that she understood from the word go that her boyfriend's close friendships with other women weren't up for discussion.
"If I wanted him, I had to have the relationships as well. It wasn't one or the other - I had to take it all as a package," she said.
The 32-year-old nurse said she doesn't feel jealous because she is always invited to go out with Christian and his "wives" and that he never hides their outings from her - including when he shared a hotel room with one of them during a board-gaming convention.
Another reason, Jen said, is because she understands that friendships can take on an added significance when someone is living far away from their family - which is true of Christian and each of his "wives".
It's a point Christian echoes.
"Claudia and Lydia have had boyfriends that have come and gone. It's the friendships that you cultivate when you don't have family in the country where you live that are really important," he said.
SISTER WIVES UNITE
Christian met his other main "wife", Lydia Sanders, while playing sport in a park at around the same time that he met Claudia, and they also quickly developed an intense and enduring, yet completely platonic, relationship.
Lydia could call on Christian when she was between share-houses and needed somewhere to crash, and when she fell sick, Christian, who is a financial analyst, helped nurse her back to health.
"At the moment, Lydia is trying to come back to Australia, so I'm storing a bunch of her stuff," he said.
Meanwhile, when Claudia's parents announced they were coming to visit their daughter in Australia from Germany, Christian said he desperately wanted to make a good impression.
"I have told Claudia plenty of times that I am nervous about meeting my 'platonic in-laws.' Her father in particular is really curious about me and I have always wanted to meet him," he said.
"I don't know if it was me or the girls who started the whole 'Wife One' and 'Wife Two' thing.
"It's not that there was any preference: they support me in different ways."
Regardless of who started that particular in-joke, Lydia continued with the theme after developing a close friendship with Claudia as a result of all the time the trio were spending together, in addition to the one-on-one time each woman had with Christian.
Lydia had been brought up in a Mormon community in Utah and despite having rejected the religion, she started to teasingly refer to Claudia as her 'sister wife.'
Claudia said she's never felt jealous of Lydia's relationship with Christian, because it is "running on a completely different level".
"I remember once when Lydia was house-sitting at Christian's place when he was away with Jen. Lydia had bad back pain and couldn't move, so I went over and helped her clean the house. We were working as a team," she explained.
BUT CAN IT REALLY WORK?
Psychotherapist and relationship specialist Melissa Ferrari told news.com.au that strong platonic friendships involving someone who is in a relationship are rare, as they can appear to threaten to that primary, romantic relationship.
This is particularly true if boundaries aren't well-established and maintained.
"Jealously is definitely the biggest problem … Creating a 'couple bubble' which puts partners in a safe zone where they always feel supported and safe is crucial," she said.
However, Ms Ferrari said that close platonic friendships could actually benefit a relationship.
"If your relationship is solid, I don't see anything wrong with you each having close platonic friends you spend time with - it can actually make your relationship stronger," she said.
The idea of a part-time husband isn't unheard of - it's a topic explored in a new book called Four Respectable Women Seek Part-Time Husband by journalist Barbara Toner. Though it's a work of fiction and set in 1919, Toner told news.com.au that the inspiration sprung from a real-life conversation she had with friends.
"We were having coffee and whingeing about our partners and how pathetic they were at some things. We said to each other how good it would be to have a part-time husband," she said.
"There is a legitimate role for a part-time husband in today's times, but whether or not it is achievable without there being any sexual content that would sabotage it, I just don't know."
Christian said that he and his "wives" are respectful of his romantic relationship, and he has made it clear to his girlfriend that there is "no confusion or overlap" - creating that "couple bubble" that Ms Ferrari alluded to.
"When it became more serious with Jen I didn't say 'Wife One' and 'Wife Two' so much," concedes Christian.
"But Jen and I sometimes joke that the wives can be a handful when they both need lots of advice at the same time. During those times, I need Jen's support as well."
CONFUSED AND BEMUSED
Christian agrees that close friendships between members of the opposite sex are rare - but he feels prejudice is to blame.
"Most people think that a guy can't have a friendship with a woman because ultimately he is interested in her sexually. To me that's just silly."
But he is also the first to admit that over the years, others have become "terribly confused" about the status of his relationship with Claudia and Lydia.
"We have been mistaken for a couple before - like when I took Claudia to my staff Christmas party. And Lydia will tell me to eat my carrots and do more exercise, so she comes across as the nagging wife," he said with a laugh.