The Lonely Hunter by Aimée Lutkin

 

"These types of connections are called 'consequential strangers,' a term coined by authors Melinda Blau and Karen Fingerman, who published a book by that title in 2009. A consequential stranger is someone who can't be categorized as a friend or even necessarily as a friendly acquaintance. They're just someone you're used to seeing in your life. Consequential strangers are co-workers, people at the dog park...there are far more consequential strangers in your life than intimate relationships, and in some cases, you'll see the supposedly unimportant people more often than your best friend."