As supply chains become more diversified and investment increases, competition to streamline inter-company supply chains is intensifying. Although several factors exist in competition,selecting the right logistics partner and forming relationships is the first step to achieving optimal logistics performance. Modern logistics relates not only to the movement of goods or products but to overall supply chain performance. Considering this context, competition within the logistics ecosystem is based on various corporate alliances, making optimization essential. Alliances and contracts are not only relationships between companies but can also be considered relationships between involved members. Relationships with contractors can be formed horizontally, vertically, or even adversarially (Jambulingam et al., 2011; Poppo and Zhou, 2013). While alliances and contracts have traditionally meant vertical relationships, as the international environment has changed and businesses have been tied into a single supply chain, long-term amicable relations have become challenging to maintain without horizontal relationships. Thus, the ideal relationship can be seen as two or more parties sharing strategic directions in supply chain management and conducting long-term transactions through horizontal and collaborative relationships (Lumineau and Henderson, 2012; Park and Hartley, 2002). Conversely, as long-term transactions continue, implicit emotions develop between the buyer and supplier, and these emotions tend to foster a desire to engage in long-term business relationships. These emotions, although complex, can be differentiated into trust, commitment, cooperation, and some others. (Myhr, 2001). As these emotions are the starting point for long-term transactions, studying logistics and supply chain performance from this starting point is necessary. Therefore, this study adopts the “triangular theory of love,” which theoretically elucidates these emotional factors to find links in the relationship between supply chain contractors and their performance. The psychologist Robert Sternberg introduced the triangular theory of love in 1986. The core of the triangular theory of love is that male–female relationships comprise intimacy, passion, and commitment and that the more balanced and established these elements are, the more sustainable a relationship can become. Evidently, this theory has predominantly been addressed in psychology and behavioral science research. However, this study applies this theory to relationships between partners within a supply chain, acknowledging that such relationships are important for firms and are related to behavioral science. Specifically, this study was conducted based on the assumption that the basic elements of the triangular theory of love—intimacy, passion, and commitment—influence the formation of trusting relationships within the supply chain and enable information sharing, among the most critical elements in supply chain management. Information sharing eliminates waste in supply chain operations and maximizes efficiency, thus creating positive tangible and intangible results. Therefore, this study’s research model was designed under the assumption that intimacy, passion, and commitment influence information sharing and that information sharing affects logistics performance, which can be considered a representative outcome of supply chain performance. This study clarifies the impact of qualitative factors on quantitative performance in supply chains and provides several insights for subsequent research and companies contemplating selecting new partners and enhancing their performance during a period when supply chains are simultaneously disintegrating and integrating.

1. Intimacy Intimacy is the psychological distance between people, referring to their frequency of contact and the degree to which they can easily contact each other. Intimacy can be considered the starting point of a relationship and the stage where mutual affection begins to form. However, intimacy without passion or commitment may lead to emotions between parties stagnating or diminishing over time. Therefore, passion and commitment are necessary for a deeper relationship. A relationship cannot start without intimacy, but progressing a relationship is difficult without passion and commitment (Kim, 2015). In contractual relationships within the supply chain, intimacy is the first factor involved in selecting a partner from numerous potential partners and developing a contractual relationship. If multiple potential partners have similar conditions, forming rapport provides a stage to discuss the initiation of a contract. If intimacy is formed through basic rapport, the relationship accelerates, playing a vital role in building trust and reducing risks and costs (Heide and Wathne, 2006; Weitz and Jap, 1995). The role of sales representatives and the relationships between practitioners in inter-company contractual relationships are represented by relationship quality, more than mere intimacy. This is because the ability to contact each other and ask for help without reluctance, even for trivial matters, plays a crucial role in forming the basic trust required in a contractual relationship. Consequently, intimacy alleviates reluctance and enhances loyalty between parties (Aaker et al., 1992). 2. Passion Passion dramatically elevates a relationship. This is contrary to intimacy, which starts out cautiously, nurtures the relationship over a long period, and can instantly stagnate or diminish (Rousseau et al., 2002). Considering its nature, responding to a relationship crisis or external difficulties with passion alone would be difficult. In other words, without intimacy and commitment, passion is likely to lead to the formation of a negative relationship rather than a sustainable one. When likened to contractual relationships within the supply chain, this can be considered a strategic alliance driven by necessity. This relates to relationships formed with radical ties centered on mutual interests. However, in times of crisis or conflict of interests, contractual relationships can easily end or lead to decreased intimacy, potentially leading to another crisis (Lee and Ha, 2023). Currently, global supply chains are experiencing rapid disintegration and integration owing to external factors. Considering this state, passionate contractual relationships can be formed to overcome immediate crises. However, passion devoid of intimacy and commitment will likely form an incomplete relationship. Hence, intimacy and commitment toward each other must be added to maintain optimal relationships beyond radical or empathetic ties. 3. Commitment Commitment is the last element of love mentioned in the triangular theory of love, and it originates from a sense of duty to sustain a relationship that started with intimacy and passion. It is a stage where sacrifice and deep understanding for the other party are possible and an element that sustains the relationship for a long time. Therefore, a complete relationship requires harmony among intimacy, passion, and commitment, and if applied to the supply chain, it can lead to information sharing, the first step for optimal performance. Dwyer et al. (1987) described commitment as the implicit and explicit promises between