Affinity, a San Francisco startup that uses machine learning to help surface valuable relationships, has raised $26.5 million. : Relationships are a tricky thing — and particularly fraught in the enterprise world, where the right connection or second-degree contact can make the difference in a high-stakes deal. That’s why almost five years ago, Stanford grads Ray Zhou and Shubham Goel cofounded Affinity, a San Francisco startup developing what they describe as a “relationship intelligence” platform.