"I felt absolutely trapped. It was a rotten situation to be in. And it's happened to me twice now." When Lucy, 26, broke up with her live-in boyfriend, she found herself in one of the UK's "hidden households", when people can't afford to move out of their home. She'd signed a fixed-term tenancy for a flat in London with her boyfriend – but had to stay living with him until she reached the six-month break clause so they could get their deposit back. And because of the limited space, there were times when they had to sleep in the same bed. You can read the full story of how it happened to her – twice – below. Becoming trapped in a tenancy with an ex is a common problem, a leading UK housing charity says. Housing and homelessness charity Shelter tells BBC Three it often hears from renters who are "grappling with the emotional fallout of a relationship breakdown alongside the legal and financial stress of not being able to leave their private tenancy." "Many people either can't afford to move out on their own, or their fixed-term contract prevents them from doing so," the charity's chief executive Polly Neate says. It's thought that 2.5 million Brits like Lucy are in hidden households – people who can't afford to move out of house shares or their parents' homes – or people stuck living with an ex-partner. That's according to recent research from the National Housing Federation, carried out by Heriot-Watt University using data from the annual Understanding Society survey of 40,000 people by the University of Essex. A separate study says young people now are poorer than they would have been 18 years ago because of rising housing costs. Research by the Resolution Foundation published in June suggests today's 18 – 29-year-olds are 7% poorer in real terms than their peers were in 2001. Georgie Laming from Generation Rent tells BBC Three it's not surprising that some young people are so quick to move in with their partners. "Splitting the cost of a room or a flat is often one of the only ways to find a private, comfortable house you can call home," she says. As one person on Twitter put it: "Our parents' generation used to stay together for the kids. Ours stay together to split the rent." Lucy's story Lucy, who now lives with her family in Bournemouth, moved in with her boyfriend after university. They lived together in various house-shares while she tried to find work in the London fashion industry until eventually, they found a place they could afford just for themselves. "I moved in with him because I wanted to – but also because it made financial sense to split the costs with him while I was going to start working in London on low-paying jobs. Had a studio been an option on my salary though, I would have much preferred that." Lucy – who was then earning around £22,000 – was paying £800 per month in rent and bills. "Money was very tight. It's always been a challenge." Unfortunately, that was the moment she realised she wanted to end things. "It was the first time it was just the two of us living together and I don't think I'd really seen the extent of the problems in our relationship when we were living with others." Lucy had to live with her ex for another three months after the split. "I didn't have the money to go off and find somewhere new and I needed to wait to get my deposit back," she explains. "There was a period of time after we broke up when we had to share the bed, which was particularly difficult. It became quite toxic. "We had a sofa which turned into a sofa bed that we took turns sleeping on – but that wasn't very comfortable, so there were times when we both wanted the bed. We even had to make a pillow wall in between us to retain some sort of independence." Lucy describes herself as "stubborn": "I was adamant that I would stay while I was paying for the flat. I had every right to be there." The living situation led to resentment on both sides, Lucy says, and even though she had friends and family who could have put her up, she had to stay nearby for work and as a base for all her belongings. Lucy, who now works as a freelance writer and tops up her income with bar and cafe work, resorted to certain tactics to keep the peace while she was living with her ex. "I had to learn coping mechanisms because you can't be in fight-or-flight mode the whole time. I had to find some calm, and ways of managing a difficult situation – like deliberately staying social with other friends, avoiding drinking alcohol in the house and doing things with my ex like watching TV together. We binged on Walking Dead." Eventually, Lucy relied on her family's financial support to help her move out. "After my first experience, I was completely put off from moving in with someone again," Lucy says. "It had been so traumatic going through it once and I said I would never live with a partner again. Categorically, no." But in 2018 Lucy found herself in an almost identical situation after moving into a flat in Walthamstow in north London with a new boyfriend. "As hesitant as I was, it turned out to be more convenient and cheaper to live together – and we didn’t have to live with other people who could make our lives difficult – so I tried living with another boyfriend." After that relationship ended, the pair decided to leave the property and abandon the deposit – and Lucy moved back to Bournemouth with her parents. Lucy says her experience with the housing market has left her "emotionally, physically and financially drained." "I think there's a lot of shame in it as well," she says. "Embarrassment and shame. It's so hard to get anywhere as a young person so failing to make a living situation and a relationship work can feel like admitting failure." Legal support in these situations can be quite limited, says Georgie Laming, but there are groups supporting renters in complex living arrangements, including Citizens Advice. "Renters unions like London Renters Union, ACORN and Living Rent are supporting renters via Facebook groups with everything from leaving an awkward flatshare to getting your deposit back," she adds. Tessa Shepperson, a specialist landlord and tenant lawyer who runs an information blog on the UK rental market, tells BBC Three that young people need to be aware of the seriousness of joint tenancy agreements and thinks education on renting should be taught in schools. "First of all, people need to realise that when they sign a tenancy agreement it is a serious binding legal agreement. People tend to be a bit gung-ho about it." But if someone is already in a joint tenancy and wants to leave, Tessa says the situation could be tricky. "The best option for someone to get out of it is by finding someone to take their place and seeing if they can persuade the landlord to agree to a new tenancy. Or if one party is prepared to pay all of the rent then maybe that's something that can be done." Or if the contract is a periodic tenancy (rolling from month to month), tenants have the right to serve notice to their landlord telling them they wish to quit, Tessa says. "If you're considering renting a flat with a partner and you're not quite sure whether you're going to stay with them forever, you might want to consider having a short fixed-term because you'll be able to end it during the periodic tenancy that follows and not before."