The 24-year-old Twilight heartthrob - who is believed to be dating co-star Kristen Stewart - said he believes in monogamy and that juggling two women 'must be hell'.
He told Vanity Fair, 'There is one thing I've never understood, why people cheat. My parents met when my mum was 17 and my father 25, they are still together and seem very happy. I grew up believing that you can be together all of your life.
'I understand the impulse, but not how you can maintain two relationships for long. And though I understand that cheating can happen to those who have children, because the stress can make people stray, I can't really understand how someone free of any commitment could possible choose to have four women at the same time. It must be like hell for a man.'