How do he address his mistress?

so if he forgets her name, he's not in trouble.

it keeps the confusion to a minimum...

Even if she was the mistress of 2 1/2 yrs?

you are assuming she is the only one...

Some men stack mistresses like so much cordwood. If he calls her Sweety, he then doesn't have to remember her correct name.

Well is he calling all of them sweetie?

No just didn't know they all had same nickname

Even a mistress trim ling time.He knows her name for sure.

Suddenly, I'm interested.

Sweetie is a term of affection, short for sweetheart. A nickname between lovers, for example honey, or love, or sexmachine or ooo err I'd better stop now.

Is that good or bad?

It's faster to type sweetie when texting then homewrecker. Takes less time.

Why do you care? What business is it of yours?

It's mine

Your threads are confusing. This was first described as having to do with a guy in the corporate office. On your next thread, it was your husband. Really? not just your boyfriend? Why would you describe your husband as a man at the corporation?

In any case, you seem not to be the only woman he is interested in.

Whether or not you are married to him, his conversation with others is his business. You do not own him.
If you have made vows of fidelity, it is important if he is fooling around, but still, what he says to other people is his business.

Somehow I doubt you have made vows of fidelity, but perhaps I'm wrong.
It sounds more like you are a nosy girlfriend.
We don't know enough to judge either him or you or "the mistress" called Sweetie.