Spanish word for a married lady's boyfriend?

Factual Questions
1

Background: Back in the late '70s a friend of mine was living in San Antonio, Texas, and about 6 months after what was basically an arranged marriage she clued me in to the status of said marriage by writing something like this:

“George is my __________. That’s the Spanish word for a married lady’s boyfriend.”

Given the nature of this communication I thought it prudent to destroy the letter, although subsequent events in my friend’s life proved it wouldn’t have mattered one way or another. But meanwhile, I lost the word!

So, anyone who can fill in the blank, please do. I mention San Antonio because I know a lot of Spanish words are used differently in different places. I am going to apply said word to a fictitious situation happening in either New Mexico or southern Colorado so I’d also like to know if this expression as used in Texas will work there, also.

2

Spanish word for married woman’s boyfriend? Muerto.

3

“Amante” would be “lover”.

4

Could the word have been “Sancho”? I had a friend tell me that’s what it means; no cite, alas.

5

Sancho

6

Well, searching for sancho and slang on google.com brings up a bunch of links, including this one.

7

Si, sancho. Although amante muerto is pretty funny.

8

It was not “sancho.” I’m almost positive of that. It seemed like it started with an M. (Not muerto! Yer funnin’ wit me.)

Maybe it was just some '70s thayng.

9

Well novio would mean boyfriend, but AFAIK it doesn’t have anything to do with whether either party is married.

10

majordomo? Like butler, maybe? In the sense of keeping house?

11

Well, there’s also mamon, which means sucker in a literal sense.