A father-of-five has revealed how taking in a homeless 17-year-old girl destroyed his family after his wife left him for their new lodger.

Tamsin Beezer, who worked with his spouse of 14 years, Sarah, 38, in a care home, had phoned in tears, saying her parents had thrown her out.

However, Wayne Gardiner, from Bristol, now says his act of kindness turned into the biggest mistake of his life – for one month later, Sarah walked out on him and the children and got engaged to Tamsin, now 18.

Wayne pictured with his and Sarah's five children Lucy, 22, Louis, 15, Chloe, 14, Charlie, 12, and Harvey, seven

Sarah pictured with Tamsin, 18, to whom she is now engaged. Wayne said he found out the couple were in a relationship after logging onto Sarah's Facebook page

Wayne, 39, only found out the truth when Sarah changed her relationship status on Facebook, which was spotted by their daughter Lucy, who at 21 is three years older than her mother's new lover.

Wayne said: 'I thought I was doing the right thing by a teenage girl who needed a place to stay. I never in a million years imagined they would get together.

'My wife [is with] a girl young enough to be one of her daughters. We are all horrified by what she has done.

'The kids are in bits. We have been married years and I never once thought she had a thing for women.'

Wayne met Sarah when they were both just 14. Sarah was 16 when they had their first daughter, Lucy.

Happy times: Wayne and Sarah together - they were married for 14 years before Sarah left him

Wayne and Sarah as teenagers. Sarah had the couple's first baby when she was just 16

Although they were young, their relationship was strong, and they went on to have Louis, 15, Chloe, 14, Charlie, 12, and Harvey, seven. They married 14 years ago.

Their family grew again when Lucy had her son Oliver, now two, with Sarah a typical doting grandmother.

Then, in February last year, they got the tearful phone call from Tamsin which has shattered their lives.

Wayne said: 'As a father of five I couldn't sit back and let a teenage girl wander the streets alone.

'I told my wife we could pick her up and let her stay with us to ensure she was safe. I had no idea I was making the biggest mistake of my life.'

Half an hour later the teenager was sitting on their sofa with a cup of tea. Wayne and Sarah gave her a duvet and pillows to make up a bed in their lounge.

Wayne said: 'It wasn't ideal, but I didn't mind. I was pleased we could help and she seemed a pleasant enough kid. We're a large family anyway, so having an extra person in the house wasn't a big deal.'

Family holiday. Wayne and Sarah together with three of their children - Lucy, Harvey and Charlie - on a break

Wayne and Sarah pictured on their wedding day with their eldest daughter Lucy

Tamsin made friends with Chloe and became like a big sister, baking cakes with her and giving her makeovers.

Lucy had previously moved out, so the younger children enjoyed having Tamsin around.

They even took her on the family night out bowling. But after two weeks, Tamsin was showing no sign of leaving, and Sarah had begun staying up late at night drinking.

I was confused and didn't really know what to think, so I just got on with looking after all the kids and left her to it

Wayne said: 'Sarah was behaving like a teenager herself, rather than a mother and grandmother. I noticed she had started smoking again. She said she hadn't, but I could smell it.

'I was confused and didn't really know what to think, so I just got on with looking after all the kids and left her to it.'

Then one morning he woke to find her side of the bed empty. He discovered Sarah asleep on the sofa with Tamsin.

Wayne claims things got worse from then. Sarah and Wayne continued to argue and Sarah spent more nights drinking with Tamsin.

Wayne said: 'I thought Sarah was just being stupid and childish.

'It did not cross my mind she had feelings for this girl, other than as a friend. I thought that, like me, she wanted to help her because we have daughters.

'Yet they were growing closer and we were drifting apart.'

Tamsin had been with them for about a month when one evening Wayne heard his son Louis arguing with his mother.

When he went to see what was wrong, a sobbing Louis said his mother didn't love him anymore and was leaving.

Wayne said when he first found out about Sarah's new relationship: 'I thought it was a joke, I think I even laughed. I looked at Sarah to tell me it wasn't true, but she just shrugged and said she was going'

Wayne, pictured with Sarah on their wedding day, said: 'I felt so sorry for the kids, they knew everyone was talking about us'

Wayne, a trainee graphic designer, said: 'I thought it was a joke, I think I even laughed. I looked at Sarah to tell me it wasn't true, but she just shrugged and said she was going.

'She got up, went upstairs and started packing a case. I ran after her, begging her to tell me what was going on.'

But he said Sarah ignored him, finished packing and walked out.

Wayne said: 'As she was leaving, I asked what to do about Tamsin.

'She told me not to worry because Tamsin had already arranged a place to stay. She had told our lodger she was leaving before telling me. But I still didn't twig what was going on. Who would?'

In the days that followed, Wayne found out Sarah had moved in with a friend, but she refused to see or speak to him.

Then he got a call from Lucy, who told him to look on Facebook. He then found out his wife had changed her status to say she was in a relationship with Tamsin.

He said: 'I was in utter shock and disbelief. I thought it must be a joke.

'How could my wife be in a relationship with a girl, let alone one younger than our own daughter? I thought it had to be a wind-up.'

He then accessed his wife's emails and was left in no doubt she and Tamsin were together.

He said: 'I had been with Sarah since she was 14 and had no idea at all that she fancied women. I broke down because I was angry with myself for not seeing it.'

Wayne revealed that the next day Louis came home from school upset that other kids were teasing him about his mother's Facebook status.

Wayne said: 'I felt so sorry for the kids, they knew everyone was talking about us.'

Over the next few weeks Wayne said he tortured himself looking at Sarah's Facebook page, which was filling up with images of her and Tamsin, kissing and holding hands.

Wayne's son Harry, his daughter Lucy, with her son Oliver, Charlie, Wayne's ex wife Sarah and Harvey

Then he heard the pair had announced their engagement on Facebook, even though Sarah was still married to him.

He said: 'I had to see for myself, so I logged on and they were showing off rings. The kids were in bits.'

Chloe messaged her mother to remind her she was still married to her father, but Sarah simply unfriended her.

Now it's been more than a year and the family have still not been able to make amends. Wayne is just concentrating on being a good father to the children and says they now want nothing to do with Sarah.

Sarah said that she did not become an official couple with Tamsin until after she had left Wayne.

She said: 'Tamsin came to stay after a row with her mum, so I said she could live with us.

'We didn't actually get together officially until weeks after I left Wayne. I moved in with a friend, nothing went on Facebook until we were officially together.'

Tamsin declined to comment.

Wayne added that he wishes he had never been Tamsin's Good Samaritan.