"And we are forbidden to discuss sex and 'walking marriage' openly, especially in the company of our grandmother or siblings," said Duoji.

"Most of the Mosuo people fall in love only once or twice. Men would no longer want to walk back and forth if they had children. They would settle down," Erqing said.

With two daughters, one aged 11 and the other six, Erqing said that his Axia was the only one in his life. "We live apart, but we promised not to betray each other," he said.

Erqing sees his daughters every day.

"My Axia is illiterate. I give my daughters after-school tutoring. They are happy with it and often come to find me. Our 'walking marriage' has lasted for 12 years. I want it to last longer," he said.

Editor: Feng Hui