So Im looking for a yaoi or shounen ai manga that isnt a rushed one shot or something completed in a volume. Id prefer something that has more that 10 chapters (ish) and allows you to get to know the characters, kinda like junjou romantica. 🙄

Not all of them are Junjou type... Anyway, long yaoi/shounen-ai I know with, hm, slow character development:
15 volumes:
Let Dai

14 volumes:
Haru wo Daiteita

11 volumes:
Kizuna
One Thousand and One Nights

8 volumes:
Koi Suru Boukun ♣

7 volumes:
Kiss me Princess
Yatteranneeze!
Vassalord.

6 volumes:
Totally Captivated

5 volumes:
Yebisu Celebrities ♣
Zetsuai 1989

4 volumes:
Complex
Koi Cha No Osahou ♣
Katekyo! ♣
Yume Musubi, Koi Musubi ♣

3 volumes:
Rin! ♣
Corsair
Mimurake no Musuko
Hidoku Shinaide ♣
Sakura Gari
Little Butterfly ♣
Rutta to Kodama ♣
Usagi Otoko Tora Otoko ♣

2 volumes:
Seven Days ♣
Castle Mango ♣
Mankai Darling ♣
Hana no mizo Shiru ♣
Sorenari ni Shinken nandesu ♣
Running on Empty

On-going with more than 10 chapters:
Hana wa Saku ka ♣
Love Stage!! ♣
Elektel Delusion ♣
Honto Yajuu ♣
Bukiyou na Silent ♣
Michiru Heya ♣
Hyakujitsu no Bara

There's more, but I'm too lazy to remember.
♣ = light ones, if you don't want to read psychological and stuff, more daily-life like Junjou.

lol dalek you beat me to most of them ~ Way to go ^.^ But yeah, most yaoi are shorter but the main ones I saw that were left out were....

Rules and Hydra by Miyamoto Kano
Also, be sure to read all the one shots ^.^ They all go together perfectly. This is like my favorite Manga Series EVER! You really get to know the characters because seriously if Hikaru Taira were real....um, I'll leave it at that... I seriously love him to death (he is the only consistent one throughout the series).

I will say that Totally Captivated is definitely one you want to read for longevity, so I am double recommending it ^.^ as well as Sakura Gari ~ However Sakura Gari is a very emotional series.... GREAT, but not fluffy.

::edit:: another one that is not yet complete that is longer is Super Lovers ^.^

Wow thanks! I have read a lot of these but I see many unfamiliar names! woo hooo ^.^ 🤣

Here's some more yaoi / shounen-ai that run more than a few volumes.
Complete
Gravitation - 12 vol.
When a Man Loves a Man - 9 vol.
FAKE - 7 vol.
Earthian - 4 [or 5] vol.
Gorgeous Carat - Kurayami no Bitoku - 4 vol. + sequels
Gohou Drug - 3 vol.
Heart of Thomas - 3 vol., classic shounen-ai
Love Mode - 11 vol.

Complete but not all scanlated
Kaze to Ki no Uta - 17 vol., classic shounen-ai
Gakuen Heaven (HIGURI You) - 5 vol.
Silver Diamond - 27 vol.
Koori no Mamono no Monogatari - 24 vol.
Komatta - 26 vol.
Ze - 11 vol.

Ongoing
Yami no Matsuei - not even shounen-ai, but lots of hugging, etc. 12 vol.
Loveless - 11 vol.
ViewFinder - 8 vol.
From Eroica with Love - 39 vol.

I haven't read Gakuen Heaven, Komatta, Love Mode, or Ze, but I've read most of the rest, and can recommend them.

There is a spin-off to Junjou Romantica, have you tried that?
Sekaiichi Hatsukoi

Breakfast Club 5 vol
Dear Green: Hitomi no Ounowa 3 vol
Hana wa Saku ka 3 vol (ongoing)

They're not super long but all of these spend a lot of time developing the characters.