The unspoken sadness and complicated nature of loving a pet who doesn't belong to you

• Many US adults are living with roommates, sometimes friends or total strangers.
• It's not uncommon for them to also have pets.
• There's something sad about loving an animal that you can't take with you when you leave.

When Rosie, a soft 10-year-old tuxedo cat with a white half-mustache, curls up on my lap, I forget about the world for a few blissful moments.

Ours is one of the more intimate relationships, human or otherwise, that I've maintained over the past several years.

But Rosie isn't my cat. She belongs to my roommate, someone I met for the first time when I arrived to take a tour of my current apartment in Brooklyn two years ago. 

My experience isn't unique. The rise in housing costs and other social and economic pressures have led droves of US adults, particularly millennials, to move in with family members or other roommates in recent years. Many of us, myself included, save money on rent by moving in with friends or total strangers — and, sometimes, their pets. 

It's a well-documented fact that pets have a positive impact on mental health, and I can honestly say that Rosie has played a crucial role in mine while her owner and I have maintained a perfectly polite-yet-distanced relationship. Still, Rosie has helped us bond (mainly over how cute she is).

Amy Canevallo, associate professor of psychology at the University of North Carolina, Charlotte, whose research focuses in part on roommate relationships, describes pets as an example of a "relational glue" that can help bring human roommates together. 

"She's helping the two of you come together around this common thing," Canevallo told me over the phone. "Even if it's not creating a deep bond, it's creating some kind of connection that would not otherwise be there."

Taking care of a pet who doesn't belong to you is a common roommate issue to navigate

Pet ownership between two people has always been fraught, like if a couple breaks up or decides to share custody, but what about those of us who don't actually own the pet friends we love?

Some pet aunts or uncles — terms I use loosely to describe people in pet-roommate situations like mine — find themselves entangled in decidedly more complicated dynamics. 

Emma Feinman, a 26-year-old membership manager at a botanical garden in Sarasota, Florida, had never had any pets (save for a guinea pig) before becoming close with her ex-roommate's cats. 

Feinman said the main reason she became so attached to the cats is because she spent significantly more time at home than her roommate, who worked long hours.

"It got to the point where I think I was more reliable than she was, so they hung out with me more," Feinman said. 

Concerned about the cats' lack of a regular feeding schedule, she began bringing home food to tide them over until their owner got home. Feinman said she made sure her roommate knew she was feeding the cats and never sought out reimbursement. It was all for the love of the felines.

Feinman's arrangement closely mirrors that of Kira Zimmerman, a 26-year-old baker in Brooklyn. Like Feinman, Zimmerman became close with their former roommate's cat, Nine, in large part because their roommate was often not home.

"I got close to Nine as a stepparent would," Zimmerman told Insider. "Nine would seek me out if he wanted attention or food" but they found this made their roommate "feel really insecure." 

This isn't out of the ordinary. Seeing your pet bonding with someone else can evoke feelings of jealousy.

"Pets are often qualified as our 'furry children' right?" said Leanne Nieforth, a research scientist at the University of Arizona College of Veterinary Medicine who studies human-animal relationships. "So in that mindset, you probably have similar feelings to your pet as you do your children." 

John Lee, a nurse in Sarasota, Florida, who lives with his close friend Harvey and Harvey's dog, Lucy, also compared dog ownership to having children — but said that his closeness with Lucy was never a point of tension between him and his roommate. 

Living with someone else's dog, however, is a bit more like being an uncle, Lee explained, as it involves a different level of obligation than owning a dog. 

"That doesn't mean I love them any less. It's just, I don't have ownership. They're not my kids," he said. In a similar way, he said, "I don't feel that obligation that Harvey probably does with Lucy." 

Jasmine Lerner, a Brooklyn resident who works as a sales representative for a beer company, has shared her cat Lily with numerous roommates — both friends and strangers. 

Generally, if one of her roommates gets along with Lily, Lerner said, she's more than happy to share the love. In fact, when she used to keep odd hours while working at Trader Joe's, she was grateful her cat had company at home.

"If my roommate was around the vast majority of the day, I would be happy if they were with Lily because that would mean she had a friend all day, and she would be maybe less annoying when I got home," Lerner said. 

Much like Lerner, Lee said his roommate was happy for the extra help and companionship. He said it's "definitely reassuring to Harvey" knowing his dog has someone like Lee who cares about her so much around. 

In some cases, pets can make a roommate dynamic more complicated — even painful

Although Lee's relationship with his roommate has remained intact throughout their time living together, the logistical and emotional challenges involved with caring for pets can destabilize a roommate relationship — even if that relationship started out as a close one. 

Shirin Bar, a 37-year-old producer living in Brooklyn, said she watched her relationship with a close family friend deteriorate beyond repair when the two began sharing space with the friend's cat. The cat, whom Bar refers to as Pishi, grew so attached to Bar that he took to scratching at the bathroom door while she showered. 

"I feel like I really formed a bond with this cat," said Bar. But things started to go south when Pishi began experiencing stomach issues shortly after the two roommates moved into their Brooklyn apartment together. 

"Every time the cat would basically go to the bathroom, I remember, the whole place would stink up," Bar told me. 

The litter box was right next to Bar's room, so she bore the brunt of the smell. She tried swapping out Pishi's food, spending her own money in the hopes that a different brand might help with the stomach issues. It didn't work. When Bar emailed her asking if they could find a new location for the litter box, she said her roommate "kind of freaked out."

The email exchange grew heated. Bar eventually snapped, she said, moving the box away from her bedroom without saying anything to her roommate. Her roommate responded by ignoring her completely, so Bar left to go stay at her partner's apartment, hoping things would cool off. 

The next day, she said, "I woke up to this text saying, 'Where's my cat?'" 

Pishi had gone missing, and neither Bar nor her roommate had any idea what happened to him —though Bar's theory is he jumped out a window left open by their third roommate. Bar felt blamed for Pishi's disappearance.

"It was really bad timing," she said. Pishi never came back, and Bar was never able to mend things with her roommate, who moved out a few weeks later.

Bar felt rattled by the experience. "This is someone who isn't a stranger who I met on Craigslist," she said. "This is a family friend, someone who I knew for years and who I really loved." 

The cat added a layer of complexities to their relationship that the two couldn't get past.

Sometimes loving a pet who doesn't belong to you can also lead to legal issues. Instances of roommates suing over ownership or claiming negligence are all over social media — some cases of roommates battling for possession of a cat have even gone to court. 

It's not all negative — having a pet that's not fully yours can prepare you for your future as a possible pet owner

One of the biggest downsides to falling in love with a roommate's pet is that you'll have to say goodbye when you or your roommate moves out — a reality I'll inevitably have to face with Rosie.

Yet the experience can also motivate people to adopt a pet of their own: Zimmerman, who hasn't yet adopted their own cat, said that they're much more open to it now that they have some experience under their belt looking after and cohabitating with someone else's.

"I've seen how they depend on their owners, and I think I'm ready for that," said Zimmerman. 

Beyond footing the typical expenses of having an animal, like buying food or paying vet bills, Feinman said that the biggest difference between owning a cat and being a pet aunt or uncle comes down to the feeling of permanence.

"I think there's more stability to it. I know that he's not just going to disappear at the whim of someone else," said Feinman, who now lives with her rescue cat Oliver.  

I know that I'll never be more than a loving pseudo-aunt to Rosie: doting, ever-present, yet with an auxiliary role in her life.

Still, I cherish every moment with her. 

I've realized I'm much more likely now to adopt or foster a pet of my own after living with Rosie. And I'd be more than willing to let my next roommate fall in love with them, too.