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Despite being quite different people, Amy* and her boyfriend hit it off immediately. They were both studying drama at university and even though he was more into techno and she loved performance art, they started going out almost immediately.

“The first couple of years were pretty solid,” explains Amy over the phone. “We went out together, we studied together, we were inclusive of each other's friendship groups.”

Things were going well, until a mouldy bathroom in a cheap student flat in London started the downfall that would eventually contribute to the end of their relationship. “And then I think things really did start to deteriorate,” she says.

Moving in together has long represented an important romantic milestone in the life of a couple. Look at literally any 90s sitcom and a major plot line will likely centre on one partner gifting a key to the other in a moment of gushing sentimentalism. Moving in with your partner represents stability and commitment, and an intention to build a life together in a shared space.

Unless, of course, you’re a millennial, and you’re spending a third of your income on rent, with little hope of homeownership in the future. In which case, moving in with a partner – and splitting your rent in half – becomes less about making a cute home (room?) together, and more about trying to stay afloat financially or live in the city of your choice. And they say romance is dead.

For Amy and her boyfriend, the decision to move in was partly made for them by the poor condition of the flat he was renting. “He'd moved into a shitty student accommodation with his friends because, of course, no one can afford anything in London," she explains. “It was so bad that there were mushrooms growing in the bathroom. I’m really sensitive to allergies, so he started staying at mine a lot.”

Either because of bad accommodation, or to save money, or both, Amy and her boyfriend continued to unofficially live together for most of their relationship, all while he struggled to get a job that would help him afford London rent. In most of Amy's homes, she let him stay rent-free. After two and a half years of dating, having lived together in different iterations for the majority of that time, and just before they were about to move into their own place, Amy and her boyfriend broke up.

“I really do think we moved in way too soon,” she tells me. “Because there was this kind of need for him to have a place, and me not wanting to let that jeopardise our relationship, I let him stay with me. That makes it really difficult for two partners who are both really young. It just created this awkward imbalance that we found really difficult to talk about.”

Does she think there might have been a different outcome had they not moved in together so soon? “I think if we'd not moved in together, things could have been different,” she says. “I'm very happy that we've broken and up and we've moved on with our lives but I think had we had that separate space, things could have worked out differently. We were just on top of each other.”

As the continued shortage of houses in the UK pushes rents up every year (rents have risen 13.5 percent in the last five years), it's unsurprising that saving money can become more important than making the right relationship decision. In some cases, this financial pressure forces couples into unlikely living situations. Remy Perrin, who lived in Leeds, decided to move in with his girlfriend and her mum after wanting to relocate to London. This was far from the ideal living situation.

“It was really awkward being in such proximity to her mum, even though I got along really well with her,” Perrin tells me over the phone. “But then as soon as there were any arguments, it was a massive problem in the house, and it was like everybody knew about it.”

“That was hard,” he adds. “I think that was one of the hardest things because everything was so much on show. Everything was so out in the open. There was no privacy.”

Perrin and his girlfriend eventually broke up – which came with its own difficulties when his living situation was so unstable. “She threw me out,” he says. “She basically bagged up all my clothes into bin bags and threw them out onto the road, and I had to move back up to Essex to my family because I had nowhere else to go."

As well as moving in with a partner, the instability of renting can affect all types of life decisions. “Having to rush or delay important life decisions can often be an unwanted consequence of our housing emergency,” Polly Neate, chief executive of Shelter, a housing charity, tells me over email. “With homeownership out of reach for most young people and a chronic lack of social homes, too many are now trapped in expensive private rentals where they face a constant battle to keep a roof over their heads.”

“To give younger renters a better start, we urgently need the government to build a new generation of genuinely affordable social homes,” adds Neate. “This would give them the foundation of a stable home and the freedom to make big life choices at their own pace.”

Stability and freedom is particularly important to Bonnie Hines, who lives in Sheffield with her boyfriend. She tells me that almost all the conflicts they have stem from an anxiety around owning a house: “Every time we have an argument about money, it's all to do with, ‘Where are we going to live in the future?’,” she tells me over the phone. “I don't want to rent forever.”

Would things be different without the pressure? “Oh, completely different,” she tells me. “Nothing's perfect and it's kind of like, once one problem goes, another one occurs. But at the same time, the problem of housing is huge to me.”

Despite renting a place just outside Sheffield for £450 a month – far cheaper than most rents in London – Hines is still consumed by the worry of never owning a house. “Whether these problems will ever be calm all depends on whether we save enough, to be honest,” she concludes, “and that's such a shit thing to have your relationship resting on.”

No wonder it's such a concern when one in three millennials are likely to rent for life (unless they happen to be one of the lucky few with parents helping out). For generations before us, a house was somewhere to invest in and make your own – often with a partner. Now, it’s a constant struggle, impacting our mental health and putting undue stress on relationships. There’s just no time to think about romance when the choice is between a mould-infested flat for £700 a month, or halving the rent with a partner you may (or may not) want to live with.

“It's so difficult, because I feel like I'm not the only one with that end goal of wanting a house,” concludes Hines. “It's reflected all over Britain really. It's really hard to get out the slump where we're all in it together. A house does provide so much for a person."