Determining current user's relationship to node author
It looks like you can use the user_relationships_load() function. The following code will load all relationship objects that exist in the system between 2 users. From there you can inspect the relationships for their type/properties and make your decision based on that:

// Set up the user ids
global $user;
$current_user_uid = $user-&gt;uid;
$node_author_uid = $node-&gt;uid;

// Set up the parameters
$params = array('between' =&gt; array($current_user_uid, $node_author_uid));

// Get the relationships
$relationships = user_relationships_load($params);