Outside of the context of a village, there are no roles and no rules.

Tarzan and Jane can be a couple, but they are not married. If Tarzan protects Jane, it is because he is hardwired to do so. If Jane nurtures and cares for Tarzan and their children, it is because she is hardwired to do so. Tarzan and Jane's cooperation as a couple is not distinguishable from the cooperation that is observed in any other species between a male and a female who copulate. In coalition terms, it is a coalition that is formed and enforced by instinct. "Fidelity" is not defined, because there are no roles and no rules and no capacity to disobey instinct.