Straight up gay

Both guys were 'straight' but turned gay. Different tone... one's contemplative, the other's comedic.
http://www.mangago.zone/read-manga/shinyuu_tte_soko_made_shinakucha_ikenai_no/
http://www.mangago.zone/read-manga/reply/

What a coincidence, same rating too. (づ￣ ³￣)づ

A few of my favourite straight x gay couples:

http://www.mangago.zone/read-manga/yoidore_koi_o_sezu/

http://www.mangago.zone/read-manga/therapy_game/

http://www.mangago.zone/read-manga/sorenari_ni_shinken_nandesu/

http://www.mangago.zone/read-manga/kitto_oujisama_ga_nante/

http://www.mangago.zone/read-manga/doushitemo_furetakunai/

(Prequel) http://www.mangago.zone/read-manga/kyuuso_ha_cheese_no_yume_omiru/ (Sequel) http://www.mangago.zone/read-manga/sojou_no_koi_wa_nido_haneru/

Also highly recommend the first manga mentioned in 1st comment :)