Yes, making shared friendships with other couples can be hard, but it might be the secret your relationship is missing.

Laura Regensdorf lives in Brooklyn with her hound mix, Pina, who has turned out to be a great conversation starter in the neighborhood.

Ms. McCabe is the author of “Making, Keeping, and Losing Friends.” When people find that they are having a hard time making new friends, they often blame their own awkwardness — some failure on their ...