Posted about this in this sub awhile back, but I'm going to try again:
I remember the main character was a young male, and he had a sister and a mother. The three of them go to a cabin or a lakehouse of some sort where they and two other families have a week of sex.
At one point, the young male gets jealous that one of the girls from another family is spending time with another male.
Any help would be much appreciated. I can't be sure, but I think the title had something to do with camping, but it turned out not to be really "camping."
I think I remember reading this on xnxx.com, but I've searched high and low there and am unable to find it.