The boy band star, who recently confirmed he is dating his childhood friend Sophia Smith, who he has known since they both attended St. Peter's Collegiate in Wolverhampton, admits he finds it hard to watch his family talk about how much them miss him in the movie.
Speaking at the world premiere of the 3D concert film in London's Leicester Square on Tuesday night, the 19-year-old singer said: "It is hard being away from our families but it was even harder to watch. That scene where my dad is talking about wanting to take me to the pub, every time I watch it , it makes me want to cry because we never hear from them what it's like for us to be away from home."
Liam and his bandmates, Harry Styles, Niall Horan, Zayn Malik and Louis Tomlinson were "humbled" by the support from their fans at the premiere, many of whom camped out for two days in a desperate bid to meet them on the red carpet.
Harry, who brought his mother, Anne Cox, and the woman who put him through to meet the judges after his first 'X Factor' audition as his dates, said: "It's insane. You never get used to it so it is very humbling. We will never be able to thank them enough."
Niall added: "We're really excited to be here tonight. This is what we do it for, the fans."
The group's mentor Simon Cowell praised them and told the crowd: "They are still the same guys we met three years ago."
Director Morgan Spurlock said it was a "no brainer" for him to take on the movie.
He said: "This is the biggest premiere I have ever been to. It was such an incredible story to tell. You couldn't write a story like this."
He added: "The biggest challenge of making the movie was this - as soon as they step out of a car, there are fans everywhere so to try to get those intimate moments, it was hard at times.
"I'm really proud of the movie and think it will make people look at them a little differently. They are so grounded and so humble."