Here's a list that checks all your requirments:
http://www.mangago.me/read-manga/me_o_tojite_3_byou/
http://www.mangago.me/read-manga/rift_conro/
http://www.mangago.me/read-manga/hana_ni_kuchizuke/
They weren't really best friends before but had something going on:
http://www.mangago.me/read-manga/roommates_young_seok/?av=2 (2nd couple)
http://www.mangago.me/read-manga/zutto_kitto/
It's a little dark and they knew each other form school but weren't best friends:
http://www.mangago.me/read-manga/the_trigger/
omg thank you so much!!!(づ￣ ³￣)づ
no problem, hope you'll like at least one of them :D
anyone has some yaoi suggestions where the MCs are bestfriends in high school (one of em hv crush on the other), got separated after that and meet again when they grew up?? kinda like http://www.mangago.me/read-manga/hatsukoi_o_kojirase_sugiru_na/