After reading more about these people, it seems to me that Mosuo sexuality closely resembles the serial monogamy and promiscuity seen in Western 20-something young professionals, or even sexually active high school students. The concept of fatherhood certainly exists.
Despite living in a culture where non-monogamy is the norm, it's common for women to maintain long term relationships that, aside from living arrangements, conform to modern Western notions of a "marriage."
The Mosuo don't have a word for jealousy, which makes sense: such a notion would preclude their whole social structure.
The Mosuo seem to display the same sexual behaviors as humans around the world, only guided by a unique social structure that's heavily influenced by time, place and social position. They have sex with multiple partners, but there's also a marked tendency to prefer single partners over time.
Despite what some people would like to believe, there's no ideal of "natural" liberated human sexuality to which it is possible for us to return. Though it's possible to find odd exceptions, an examination of the relevant history will reveal both infidelity and sexual jealousy to be practically universal across time and culture. Humans form pair bonds and cheat opportunistically.