If anarchy is simply a principle of relating with another human being, then how do you apply it in a relationship with say your partner?

In a marriage, both needs to coexist in a shared space. The core of anarchy is optimization and maximization of individual freedom. Each person should should therefore be treated as an autonomous individual. There has to be conversations to uncover shared values and negotiations on differences to achieve a compromise. If not, then it is better for two entirely different and even conflicting persons to not be together.