Not when people choose to marry trees.

id assume this would come from people getting married, divorcing, and getting married to a new person all within the same year

Three person marriages exist

Someone married a train station, someone else married an historical landmark to keep it from being knocked down, and a third married a tree. Read fark dot com

Polyamory?

Not necessarily. That could just be the number of couples who got married, that doesn't necessarily include their partners since only one person counts for a "couple" here. 4,123,651 couples could have gotten married.

A former co-worker is married to himself.