http://www.mangago.zone/read-manga/my_last_love_scenario/ this is the second book though.
Such a favorite. http://www.mangago.zone/read-manga/mou_ichido_nando_demo/
Dubcon in the beginning, but their story here spans 20 years. http://www.mangago.zone/read-manga/ace_no_kyuujitsu/
Similar to Mou Ichidou... http://www.mangago.zone/read-manga/kowagaranai_de_soba_ni_ite/
Can anyone recommend a good yaoi centered around a long term relationship?
Like when the story starts, they're already together and you get you see their ups and downs as a couple.