Actor Robert Pattinson says he doesn't understand why...

Actor Robert Pattinson says he doesn't understand why men cheat on their wives and girlfriends.

The 24-year-old, who is in a relationship with his Twilight co-star Kristen Stewart, said he had grown up believing people can be together for their whole life.

"There is one thing I've never understood, why people cheat? My parents met when my mom was 17 and my father 25, they are still together and seem very happy. I grew up believing that you can be together all your life," Pattinson told Italy's Vanity Fair magazine.

Robert Pattinson"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 possibly choose to have four women at the same time. It must be like hell for a man," he said.