In contrast to latent variable models suggesting a common etiology, network theory proposes that symptoms of psychopathology co-occur because of direct, dynamic associations among them. We examined how symptoms associated with borderline personality disorder, depression, and anxiety mutually reinforce one another over time, forming a network. We further identified symptoms that drove the network by exerting the most influence on other symptoms. Participants were 37 undergraduate students aged 18 to 26. Following baseline assessment, participants were prompted to answer a Qualtrics-based survey of current symptoms of BPD, depression, and anxiety twice daily for 40 days. Multilevel time-series network analyses were conducted with (a) BPD symptoms alone and (b) BPD, depressive and anxiety symptoms. In the network of BPD symptoms, momentary interpersonal difficulties predicted later dissociation, which predicted later affective fluctuation at the within-person level. Dissociation exerted the strongest influence on the overall symptom network. When depressive and anxiety symptoms were included, the networks identified several cross-disorder connections, such as anhedonia and feeling tense, which highlight potential pathways that describe the comorbidity of BPD with anxiety and depressive syndromes. Overall, cognitive symptoms and dissociation were identified as the most influential symptoms across the networks. This study indicates that BPD, depression, and anxiety symptoms may mutually reinforce one another concurrently and over time. Cognitive symptoms exert the highest influence on the cross-disorder networks, such that they influence BPD, depressive, and anxiety symptoms. Our results support the need of targeting cognitions in the treatment of comorbid BPD.