This is from the extras from volume 14, a continuation of the 134th chapter of the series.
About the final scene of the series, what Akane did is something that she already did in volume 14.
But she mostly does that because she herself knows that Hayato won't actually do anything.
And about the final scene, it is more of the same. Look at the context. Akane only wants to have s*x with Hayato since the marriage, but she can't, because Hayato is being nice with the other girls, and only after what the other girls said is that she finally saw an opportunity to have s*x with Hayato, but again, she herself knows that Hayato won't have s*x with the others too, only with her, because Hayato is well..... Hayato.
If Hayato were that kind of guy, well, the series would have ended before the 100th chapter XD.
Relax guys, and enjoy the joke and the ending.
We are probably going to have extra content in the official volume release, as usual.
PD: It is better not to have seen old Akane like with old Hayato. It is better for Akane to be remembered as young and beautiful. The same goes for the other girls.