Final answer:
Happiness in relationships is related to having a partner with a similar personality, supported by the concept of homophily and theories of love and relational satisfaction.
Step-by-step explanation:
Research indicates that happiness with one's relationship is related to having a partner who is similar in personality. This concept is supported by studies which show that we are attracted to people who are like us in terms of background, attitudes, and lifestyle due to the ease of forming connections and relationships when commonalities are shared. This preference for similarity, known as homophily, extends to various types of relationships, including friendships and romantic partnerships. Moreover, the presence of intimacy, passion, and commitment, as described by Sternberg's theory of consummate love, is characteristic of a healthy relationship, while social exchange theory suggests that the benefits of relationships often include happiness, fulfillment, and even good health. All of these factors contribute to the understanding that partners with similar personalities tend to have more satisfying relationships.