Basically the ending is very open ended in that in vol 17, which is pretty much the last novel, the MC decides to go an live while working as a doctor on an island with a few hundred inhabitants at the same time it's a bit of a harem ending where all the heroines are sort of in a relationship with him and free to go visit him on the island but at the same time Masuzu the "main" girl has forced the MC to sign a contract to stay virg*n for life.

After this the author put out vol 18 which was a sort of epilogue story set 11 years after vol 17 so their all 29 years old now and in it it's explained how everyone went on with their lives and the MC has stayed a virg*n for 11 years with most of the girls visiting from time to time except for Masuzu who has completely cut contact with him for the past 11 years. Then the MC asks for a get together with everyone when they turn 30 so the next year but everyone shows up shortly after. Stuff happens and it's revealed that Masuzu is super rich and successful and has been playing pranks on everyone for giggles over the last 11 years, among the pranks is that she for instance got a patent on the name of Ai's manga/anime so she's forced to redo all her works, she's also been ignoring the MC for 11 years as a prank but has been stalking his every move during this time.

There is some other stuff like the the women wanting to sleep with the MC to which he agree's, sort of, but refuses in the end since they don't have any cond*ms. There is some more stuff but basically it's a harem ending again though at the very end it's revealed that there are cond*ms there now but that Masuzu through her connections and as a "final" prank on everyone has made sure that there are holes in every cond*m sent to the MC and since their on an island there is no chance of getting any other cond*ms. Then it pretty muchs ends at that with it being implied/hinted at that Masuzu's final prank is to have the MC get all the girls pregnant before they turn 30. But again nothing actually happens in the story and it's just implied the MC will get them all pregnant. Though they might as well stay virg*ns for life so who knows.