I think Ejima Eri wanted to do a very specific type of plot, maybe she was only interested on representing the heavy conflicts at the very beginning of this relationship, so she decided that to represent the happy-go-lucky stage of the relationship was superfluous, so she finished the series when she thought that all of the big early problems were solved. Taking all of the above into consideration seems to give the answer that the ending was effectively very fitting, so kudos to Ejima Eri for doing what she wanted and not taking the easy way, even knowing that some tards would throw shit to her for not doing what THEY wanted, like a kiss on the grand finale.