That pre-marriage affair was just a goodbye kiss.
Kisses, HJ, BJ, intercourse, of course.
Then again, she may be telling the truth.
Your phone call let the air out of her resolve, her Last Tango with her EXBF.
She ended any and all further love making with this guy, she went into the bathroom and bawled her eyes out and did not do more.
I doubt this. She went there with the intent of performing the Full Monty with this guy.
Oh, as a goodbye gesture, mind you.
She likely laid on the floor because, the EXBF disappointed her again. He would not commit, again. That is why she cried.
I suspect your 'then fiancee' (at that time) was not sure what she wanted and was going to test drive him one more time.
He failed the test (again) and she came back to you.
It could have gone the other way, mind you.
It was a close decision.
That is why she was never remorseful.
She thinks herself the prize, two men wanted her, and you got her, be grateful.
She loved him more that you, that is why she took such a chance, left you in the lurch and took advantage of your feeling.
In the end, she re-realized that you were a better pick for a husband, so she so kindly 'took' you back.
It was a very hard decision for her.
I suspect, the EXBF, had done little more to shine in her eyes. But, she was a-hopin'.
She certainly had feelings for him and made no apologies for this.
Her saying that if you bring it up again, (means) that she still regrets making that original decision. She regrets losing him.
She still has insufficient feelings for you.
And you better not forget it, or your are gone!
The best medicine for her at this point is just to file for divorce.
If she asks why, tell her that she has lost her 'luster', and that she has few if any redeeming qualities.