The likes of clarity and efficiency are good communication concepts for designers and evaluators of business communication tools. They make little sense, however, when the design context of an interactive system is the support of a personal relationship. What matters then is that people feel they are ‘there’ for one another. This paper describes a new way of understanding Social Presence in technologically mediated communication by relating it to a well-established psychological relationship construct: Closeness. We propose a model whereby an individual’s long-term feeling of Closeness to others is influenced by communication events that are invested with a sense of Social Presence, as a function of the background level of psychological Closeness. Thus each communicative act, and its associated feeling of Social Presence, has an impact on the feeling of Closeness. We report a three-week-long study during which 18 participants reported daily ratings of Closeness, and communication-event ratings of both Closeness and Social Presence. Our findings are consistent with the model we propose, suggesting that systems for intimate relationships require consideration of both Social Presence and Closeness. We further consider methodological and measurement issues in the realm of personal relationships, and the expanding remit of HCI design as an active contributor to the world of experience and feelings.