Many human societies lack sexual jealousy; controlling of someone else's sex life is akin to controlling their autonomy, which is sacred to everyone. In these societies, people use sexual relationships with several people to cement social bonds.
A major difference between humans and virtually every other species is concealed ovulation. In other species, males can tell when the females are fertile, and they will only have sex at those times. However, in humans, males cannot tell when females are ovulating, so humans have sex anytime during the cycle. This also makes patriarchy effectively impossible in the species. In patriarchies, there is an obsession with paternity; in humans, males can't tell who their children are because of concealed ovulation, so the only way to figure out who their children are is to severely restrict the autonomy and sexual freedom of women, which makes for a very unhappy society, not to mention decreasing the creativity, intelligence and freedom of the entire species.
As I said, not all societies do this. In these groups, mostly matriarchies, all children are loved by all adults. No one would say, "That's my child. You don't tell it what to do!" Matriarchies are also much more male-friendly places to live in, as males aren't held to an impossible ideal. They are more relaxed, happy and peaceful than men in patriarchies, who are severely limited by what emotions they can express. People value cooperation more than competition, and see the sexes as complements to work together, not opposites to fight and triumph over each other. Neither sex is inherently better or worse than the other, because both are necessary for procreation and building societies.
The Mosuo in China lack marriage altogether. They also lack an idea of a father. Men raise their sisters' children along with them. Anyone can have sex with anyone, there is no sense of commitment, and no one gossips about anyone's sexual flings. Sexual fidelity to them is shameful because it's an attempt to control what someone else does. And their love for each other is no less than love in other societies; they don't tie love and sex together. They can have a one-time fling, have sex with more than one man a night, or have a decades-long relationship with one person; it's everyone's personal choice. They also lack war, murder, rape, theft, child abuse and violence.
So sexual jealousy is not universal, nor is violence in humans. It has to be taught and conditioned into a group.