You searched for: “polyamorist
polyamorist (s) (noun), polyamorists (pl)
Someone who has more than one open romance going on at the same time.

It should be noted that poly means "many", not "more than one".

—From new words and senses from the new 2006 update of
Merriam-Webster's Collegiate® Dictionary, Eleventh Edition.
This entry is located in the following units: amat-, amor-, am- (page 2) -ist (page 52) poly- (page 2)