Yeah I did not enjoy the other one, pretty sickening actually. It seemed like the one character was cheating but there was nothing about that addressed at all. Unless the original pair were never together but that seems to go against how the main chapters were written.
Agreed, why did they have to ruin a good doujin with this shitty chapter?
These two were not shown interacting in the slightest in the original 4 chaptera, so it feels incredibly out of place, especially after the end of the main story, where it shows that the two protagonists are still together.
I hate it when manga artists ruin their stories just to draw sex.