Looking for a story I read a while back. The usual search hasn't brought it up so I am posting here.
Here are the facts of the story that I recall
1. Main character is a guy, maybe mid to late twenties or possibly early thirties, though I don't recall if his age is ever stated.
2. He meets and dates a young woman in the city where he lives. She has a younger sister. The sisters' parents are strict and fundamentalist religious people.
3. The sisters also have an uncle who is much more liberal than their parents but who also fiercely protects them.
4. The guy and his girlfriend decide to go on a vacation somewhere along the coast. I don't recall now why or how but the girlfriend's sister comes along as well. They are the coast at least a week, possibly longer. It might be Spring break but I don't recall for sure.
5. While there they meet a number of other young women and maybe a couple of young men. These other people start to hang out with the 3 (guy, girlfriend, girlfriend's sister).
6. The main character guy has sex with his girlfriend as well as the sister and 2 or 3 of the other women during their stay. They are staying at a rented house of some sort that is along the beach. In fact the whole group trade sexual partners while at this beach house.
7. When they return from vacation to the city, the sister's parents issue some sort of ultimatum to the younger sister and so she leaves and moves in with her older sister and the boyfriend.
8. The main character guy has an estranged sister who is mad at him since their parents died several years prior. He was executor to the estate and had control over how much money his sister got, which she resented. Now years later he attempts to reconcile with his sister and at first is rebuffed but eventually they connect. He invites her to visit him in the city where he lives with his girlfriend and her sister. She does and the 3 women and the guy have sex multiple times over a period of days and weeks.
9. Eventually the girlfriend and her sister both get pregnant by the guy and he decides to marry both of them. One of the other women from the coast vacation visits and it is revealed that she is also pregnant from her sexual relationship with the guy while they were all at the coast. He also decides to marry her.
10. The guy eventually buys a large house in another town where he, and his wives can live and where his sister can also live.
11. The main character guy's name might be Jason or Justin or Jack or John but I don't remember for sure and it might be something else entirely. I don't recall any of the women's names.
12. The story is moderately long. It has multiple chapters but I don't recall just how many.