Many, many, many duplicate contacts of only select contact cards

It appears this has been asked a number of times even in the last 12 months. Some "Solved" responses have suggested selecting the duplicates and deleting them. Geez. That addresses the symptom, not the disease. There is an underlying issue with Contacts, it seems, that replicates some contacts - again and again and again and again and... (got the picture?) I have over 500 duplicates of some of my contacts. My Contacts collection has over 13,000 records; I'm sure I have well under 800 real contacts that I've collected since I bought my first Mac in 2004. WTF?!? So in iCloud, I can scroll my contacts from the As to the Js, and when I reach my own contact card (of which there are over 500) I get the spinning wheel and I wait. And wait... If I could search successfully for the duplicated cards, I could delete them, and cross my fingers that this doesn't happen again. Ugh - so many to search, select, delete, and synch. I have over 500 occurrences of my ex's contact card - who wants to see THAT!?!? Each of my devices (15" MBP retina mid-2012, iPAD 7gen, iPhone XS) is consistently problematic.

There seems to be a bigger problem here, expressed in many different ways in the forums, that needs to be addressed. Can anyone point to a definitive solution and/or fix?