I came across a story late in 2020 or earlier this year, where an 18yo guy had a single mother who was pregnant again.  Unbeknownst to him his 19yo bodybuilding friend ended up having an affair with the guy's pregnant mother.  Does that sound familiar to anyone?

Seems interesting. Do you remember where was it hosted?

I wish I did. I generally only muck about on Literotica. But I can't see to find it there.