Research exploring therapists’ experiences of working with infidelity is limited, yet infidelity is a frequent presentation, and one of the most challenging for therapists to work with in practice. The aim of this study was to construct a theoretical understanding of how therapists experienced themselves when working with infidelity. Eight experienced couple and relationship therapists were interviewed about how they experienced themselves inter-subjectively while working with presentations of infidelity. The data were analysed using a Constructivist Grounded Theory methodology. A core process was constructed from the data ‘Absorbing ambivalence’. Three sub-processes, ‘embracing ambivalence’, ‘tuning into ambivalence’, and ‘assimilating ambivalence’ were conceptualised as constituting this core process. These processes were theorised as emergent, one leading from the other, circular and interdependent, comprising a process model of how therapists experienced working therapeutically with infidelity. The conceptualisation of a process model has potential in helping therapists to make sense of and understand their inter-subjective experience when working with infidelity. It also offers a tool for use in reflexive supervision and in the training of therapists working with infidelity. As a result of this investigation, future research is encouraged to further explore, with the aim of understanding, the processes involved in how therapists become aware of and manage the influences of the wider sociocultural context when working with infidelity.