The rationale behind the API is public data. i.e. anything that is visible even if not logged on. Don't think that includes friends so unlikely.
Endpoint for List of Friends
The list of friends of a player is actually visible to the public, so in theory there might be an endpoint.

@SiriusBacchus A good place to search an answer on the question like that: https://www.chess.com/news/view/published-data-api
Hi,
Is there an Endpoint to get the list of the Friends of a player?