some long yaoi's with good plot ones i'm reading or have read are

okane ga nai
junjou romantica
Fake
koisuru boukun
sex pistols
totally captivated
crimson spell
honto yajuu
haru wo daiteita
sekaiichi hatsukoi
g-defender
brother x brother
gokujou no koibito
you're my loveprize in viewfinder

i'm looking for some more to read any help will get a Big thank You

long yaoi:

Hari no Hana
Love Stage
Super Lovers
Saezuru Tori wa Habatakanai
Elektel Delusion
Hua Hua You Long (aaaah, so HOT)
Himegoto Asobi
Hyakujitsu no Bara
Vassalord

these are some of my favourites, and, quite frankly, classics (in the yaoi world, haha). so you just about have to have read these at least once!!! you wont regret it!

and a really great long shounen ai I'm reading is Asterisk .

hana wa saku ka
complex
yuuutsu na asa
sakura gari
let dai----> good shounen ai 🙂

kekekeke

What I think are the more complete threads recommending multi-volume yaoi. I put them together from other posts. A lot of the suggestions are repetitive.

Long, multi-volume yaoi
[Looking For]UnlicensedYaoi with Multiple Volumes
Yaoi with long story or shounen-ai
Looking for 10+ vol yaoi/shounen-ai
looking for any yaoi or shonen ai manga with various volumenes.
Where can I find long yaoi with good art?
Long Romantic Yaoi Manga!!! (Like Crimson Spell or Junjou Romantica)

It looks like it's time to create a tag "Multi-volume BL", for any yaoi or shounen-ai that's longer than 2 or so volumes. If we use 'BL' in the tag, we can include both shounen-ai and yaoi, and then anyone who wants to do a search can exclude one or the other (since a lot of shounen-ai fans don't like yaoi and vice versa).