What happens to the manga after the anime?
The anime barely adapts anything from the manga and adds an anime original rival character for the final episodes.
Although the last couple of arcs were already terrible the original manga got the ending it deserved and that could've been the end of it. The sequel(college arc) is where it really went to shit: we get a mostly new side cast (old characters only get cameos) and the only old character that still has a strong presence is Iris the Ranko replacement. The harem nonsense is dropped which you'd think would mean they'll progress their relationship, but that doesn't happen at all and instead every arc makes me question why are they even still a couple. The big question the original manga left (what does Junichi want to do) is slowly getting answered and unsurprisingly it has little to do with Yukana who has her own career path. The only good thing is that the two new side girls aren't interested in Junichi: so that we have Iris who hates him for constantly (accidentally) harrasing her; Karin (the mangaka) who is more into Yukana and thinks MC is lame, he kind of became her social media manager; Gokomachi who actually is a tertiary character from the original manga that comes from Kyoto and is an heir to a wagashi shop(again making her someone closer to Yukana who is making western style confectionery) who happens to be his neighbor while in college. Unfortunately the core of the series is still the same and all it is used for is to write more and more convoluted ways for the main couple not to have sex. (Karin "dating" Yukana, Junichi pretending to date Gokomachi, Junichi using Yukana to promote Karin's manga twice, Junichi forgetting he has a girlfriend, whatever the fuck this arc is)