Relationships form the core of connected learning. In this study, we apply and extend social network analysis methods to uncover the layered network structure of relationships among Fanfiction.net authors and reviewers. Fanfiction.net, one of the world's largest fanfiction communities, is a space where millions of young people engage with written media, connect over shared interests, and receive support and mentoring from a distributed audience. Does an affinity space such as Fanfiction.net have the same structure as social networks Facebook and Twitter? We applied k-means clustering on millions of relationships to determine that Fanfiction.net has 2 to 3 layers, in contrast with the 4-layer structure of Facebook and 5-layer structure of Twitter. In addition, we conducted a large-scale machine classification of Fanfiction.net reviews to reveal the types of mentoring exchanged in each layer. Our findings show that the relationships where reviews are exchanged most frequently are most likely to contain substantive reviews. We discuss implications of these findings for the theory of distributed mentoring as well as the design of online affinity networks.