Any yaoi mangas with actual relationship development that is good? And not just some point...

Blue sky complex

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

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

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

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

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

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

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

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

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

http://www.mangago.zone/home/mangalist/124499/

also wanna add Totally Captivated and Ze to that list

Don't know if it's what you meant, but check out my "Slow pace" list http://www.mangago.zone/home/mangalist/36755/ the romance is built in a believable way (usually xD)