Kaimax wrote...
Doujins rarely exceed 50 pages.
What you are reading is a hentai Manga tankoubon, which is a collection of different manga titles from usually the same author. So you can't really say it's the longest just because of the pages.
You need a tankoubon that actually has one continuous story.
Some that came to mind is Erect Sawaru's "Pandra series" and Shiawasu no Okina's "Shining Musume Series"
Pandra actually has 2 volumes (200 pages each), and a 2nd Saga Story. While Shining Musume has 7 volumes with 200 pages average.
Let's add Sessyu Takemura's Take On Me and Kensoh Ogawa's Honey Blonde as well, if those two count.