Seems to mainly fit criteria: https://www.mangago.zone/read-manga/timeless_melody/
Some problematic/dated elements but fits some of your criteria, distinct historical feel: https://www.mangago.zone/read-manga/tomoi/
hey so this isn't the one you asked and this is more about queer ppl in general instead of bl but it has the same themes and is one of my all time favs so try it :)
https://www.mangago.zone/read-manga/shimanami_tasogare/
this one is good too
https://www.mangago.zone/read-manga/until_i_meet_my_husband/
until I meet my husband is based on a real story of a japanese lgbtq+ activist
Bl mangas based on reality. Plot occurs maybe in the 90's or past that. Shows how hard it is to accept own sexuality, coming out, homophobia, disappointed parents, being with the one you love.
Something more realistic based on society. If it has a sad ending bring it on