Answer:
Respect - Both partners must respect each other in the relationship and treat one another how they would like to be treated. This would ensure that both partners treat each other in a way that will keep the relationship healthy and strong.
Trust - A relationship without trust is doomed to fail because there will be a lot of fighting and negative feelings towards the other partner because partners will be suspicious of the activities of the other partner.
Compromise - Human beings are never the same so people in a relationship will not always behave the way the other partner wants or have preferences that are liked by the other. Compromise is needed in such cases to move the relationship forward.
Communication - Humans are social creatures so if a relationship is lacking in communication, it is as good as dead. Partners need to be able to communicate their thoughts and feelings to each other so that partners know how to act to bring the best out of the relationship.