Straight turned gay

https://www.mangago.me/read-manga/straight_kun_to_gesu/
https://www.mangago.me/read-manga/mizu_numuru/
https://www.mangago.me/read-manga/kocchi_muite_ai/
https://www.mangago.me/read-manga/hoshi_wo_kazoeru_koto/
https://www.mangago.me/read-manga/ichika_bachika/
https://www.mangago.me/read-manga/shirouto_yankee_kikiippatsu/
https://www.mangago.me/read-manga/shitsuren_junky/

https://www.mangago.me/read-manga/grab_the_stars/

https://www.mangago.me/read-manga/crossing_the_line_1/

https://www.mangago.me/read-manga/tomodachi_engagement/

https://www.mangago.me/read-manga/abnormal_rommate/

https://www.mangago.me/read-manga/soredemo_yasashii_koi_o_suru/

https://www.mangago.me/read-manga/yamada_to_shounen/

https://www.mangago.me/read-manga/yasashii_koi_ga_sodatsu_made/

https://www.mangago.me/read-manga/itsuka_no_koi_to_natsunohate/

https://www.mangago.me/read-manga/sorenari_ni_shinken_nandesu/

https://www.mangago.me/read-manga/sensei_wa_butchozura_shite_yatte_kuru/

https://www.mangago.me/read-manga/motoyan_papa_to_hitsuji_sensei/

https://www.mangago.me/read-manga/ore_to_joushi_no_kakushikoto/

https://www.mangago.me/read-manga/crackster/

https://www.mangago.me/read-manga/goriyou_wa_keikakutekini/


I haven't read all these, but I saw some summaries and tags that says that one of them is straight then turns gay. Hopefully you find what you want in these stories :)