Apocalypse setting
After a worldwide catastrophe (deadly virus or sth.) some survivors are forming a group.
One man and some women with different social background and education.
If he is self confident, he can lead the group, while some of the woman try to benefit from a good relationship with their leader. Others may fight their loneliness or just want to get hugged.
Science Fiction / Alternate Universe
A setting in an alternate universe (partly inspired by an episode of a tv series)
Due to a genetic defect, the birth rate of males is low (maybe 1 to 1000) for some hundred of years, and is still decreasing. (test-tube fertilization isn't invented yet or doesn't work properly)
In this centuries society changed.
Women are living together and lesbian sex is just normal.
Sexual contacts with men are restricted. Women above 18 can apply for a sexual contact wit a man, which could granted within their fertile days. (to keep population constant, maybe the most women only have sex with a men once in a year)
In most lands men have to live in fertilization camps (kind of male whores), where they have to "serve" their clients (maybe 2 or 3 per day). Creampie is statutory.
For persons of high society it could be easier to get an appointment (imagine a 50yo senator with her 48yo wife (and maybe their 18yo lover or daughter) meeting a man just for fun, though they aren't fertile during the visit. Maybe some VIPs could have their own man at home...)
There are still wars, but now they are mostly raids to steal men from other countries.
Besides that some rebel groups fight against the authorities and try to free the "stallions". Then they live with them in the underground and have a voice, who they want to fuck. In this groups also different sexual positions are allowed (anal, "waste" of cum, ...), though it depends on the specific group (controversial issue). Some groups fight for the human rights (of the male whores), others just want personal benefits.
At the start, i could imagine two options:
1. The protagonist lands in that universe as a side effect of a failed experiment. (science fiction)
2. He is born in that universe and grew up in a male boarding school (seperated area of the fertilization camps). At age of 18 he gets a maturity party, where he will have sex for the first time (maybe with a group of girls to choose from)
In both cases the protagonist could switch between fractions (get caught by authority, get freed by rebels (, get found by normal citizen after landing in the alternate universe)), and love and/or hate his situation.