The proper role of the human female is to remain chaste until guaranteed a secure and stable relationship from a human male.
Human females that deviate from this role will be considered "spoilers" to the main group of chaste human females. These spoilers lower the bar for the main group. They are the females that engage in sexual activity without the guarantee of a secure and stable relationship. They give human males the idea that all females should engage in sexual activity when prompted. This then makes it hard for chaste females to secure a stable long-term relationship due to new found expectations about human females brought about by the spoilers.
Not only do spoilers make entering a stable long-term relationship difficult for chaste women, but they make maintaining in-progress stable long-term relationships difficult. Spoilers are the ones that engage in "cheating" with a human male that is already engaged in a long-term relationship. Without spoilers, the human male would not have a likely ability to engage in sexual relations outside his current relationship.
One can observe in human females the tendency to show anger towards the "spoilers" that engage in sexual relations with their mates. One might find it odd that in some instances more anger is shown towards the "other woman" than to the male mate when an instance of cheating is discovered. But when looked at with the idea of the "other woman" being a "spoiler", it makes sense.
Human females gain control over human males mainly through sexual gatekeeping. They have control when they are in charge of when human males can and cannot have sexual relations. Spoilers degrade this ability and put the power in the hands of human males. Spoilers thus remove power from human females as a whole and thus human females are rightfully angry at spoilers.