Many researchers have tried to understand why some learners engage in and others disengage from mathematics by exploring learners' mathematical identities. Significant others (i.e., teachers, peers and family members) offer learners' different opportunities for mathematical identity support, but no study has explored their collective role in supporting or constraining learners' identities. In this paper, we explore how relationships between high school learners and different groups of significant others shaped learners' narrated mathematical identities. Fifty Grade 10 learners responded to a mathematical identity questionnaire. After analysing the results of the questionnaire, six learners were purposively selected for a semi-structured interview, and the interview data were analysed thematically. Identities are described as robust-leaning, mixed or fragile-leaning, depending on learners' narrated confidence, persistence, beliefs and sense of belonging to or exclusion from mathematics communities. Relationships with teachers, peers and family members are described as robust-enhancing or fragile-enhancing, depending on the kind of identity encouraged by the relationships. The findings show that many learners narrated fragile-leaning identities, and all the learners showed some robustness and fragility in their identities. The more groups of significant others a learner developed robust-enhancing relationships with, the more likely the learner narrated a robust-leaning identity. We argue that understanding learners' identities requires understanding their relationships with the three different groups of significant others as a collective.