It's called "Philip's Mom" and my friend Mike McGifford wrote it.
https://storiesonline.net/s/30137/philip-s-mom?ind=1
He also wrote "Cunt Next Door" but he gave me permission to edit and post it up for him/finish it.
If you liked that one - you'll love this one.
The working title was "Mom's Tits" which I thought was brilliant in it's simplicity.
This is really an epic story about a family that loves each other, isn't obsessed with sex but at the same time - sexuality plays a central role to the story.
There are secrets within secrets, and lots of nuance.
I can't tell a story as good as this one, and it really is getting under-valued/not noticed as it should be.
I will warn you that the first chapter is basically HUUUGGGE! You may want to take it in bite-size chunks.