And in a relationship, we have normally 2 parts, the one part representing the female energy and the other representing the male energy. "Partner" comes from the word "part".
They can start a relationship as parts and be able to come together as lovers.
Also, each one of us no matter male or female is woven by both energies. In Yoga these energies are going through 3 main energy channels: Ida (-), Pingala (+), and Sushumna (=).
The Sushumna channel is balancing both energies and is therefore at the central pilar - the spine.
As there is an energy channel that is balancing both energies in our body, so there is also a way to harmonize ourselves with our different part of ourself.
And this can be a challenge because the other person has a unique energy flow, other chakras (energy centers) are more active and its different intensity.
Thatswhy the path of Tantra is to uniting the opposite, none of them can make the whole without the other part, it is no good or bad.
When both parties are able to achieve a state of dynamic equilibrium (balance) the Harmony between them is born!
As both partners are going in society, having exchange with different people, obstacles in their life, it is needed constantly that they come to their harmonious living.
One of the basic exercises in Tantra, that can help them is just having silence eye contact in a quiet room in a meditative state.