Without even thinking, I've created a side plot in my next ebook. I'll explain but not try to ruin my story's plot

A is the good guy who is assisted by B and C (who are the tg characters)

D is the bad guy. He's assisted by E and F.

As I write the story

C and F do similar work for their bosses. F is a scumbag who A has personal reasons for hating that person.
D is seriously unhappy with F.
D has a lady friend R (Never seen but often mentioned for the first 1/3 of the story), R dies

C and R are a similar type of woman (What type? Their breast size? The color of their skin? They both use the same mouthwash? They both give to the March of Dimes? I will let you guess if one of these or something totally different is the clue)

I've built this all up to the tune of about 68,000 words and the climatic part is underway when I realize

The plot I have set up has left me the possible subplot- D is attracted to C soon after they met while D tries to do business with A. C could replace F and be his new lady friend at the same time. C would still towards the goal of eliminating D (and the project he's working on) or not do that but this makes D more tempted by the bait that will be used to destroy him because he wants C.

At this point I can write this into the story without changing anything.

I've been working on a story for a month and developed a subplot without even thinking about it. Until today.

On a smaller scale than this, I've twice written little things into a story and then at some time later found out they coincided with reality. Namely the timing of a television broadcast and where a certain yearly sporting event was to be held.