im looking for long shounen/senien romances like Maison Ikkoku by Rumiko Takahashi.

I's, Ichigo 100%, Good Ending, Pastel, Domestic Kanojo there are so many that it is hard to think of off the top of my head.

Oh, I have so, so many for this... Here's my highest recommendations:
Dengeki Daisy
Horimiya
Love So Life
Meteor Methuselah A bit heavy on other stuff though, like action and so on...
Kisu yori mo Hayaku
Koi Kaze Taboo and kinda depressing in places though...
and
Keishichou Tokuhanka 007

I hope some of these suit your tastes. 😀

Bacchanals, to arms!
Quote of the Year (2017): "The mind is its own place, and in itself can make a heav'n of hell, a hell of heav'n." -John Milton

read all of these 🙁

I feel your pain... try looking through my Great Read's list on my profile. Almost everything I've got has romance in it at least a little bit. Might be something you haven't read yet that fits.

Bacchanals, to arms!
Quote of the Year (2017): "The mind is its own place, and in itself can make a heav'n of hell, a hell of heav'n." -John Milton

Melo Holic
Taiyou no Ie shoujo but give it a try
Angel Densetsu
Hana to Akuma shoujo but give it a try
Hoshi no Samidare
Superior + Superior Cross
Chrno Crusade
Karin
Magico (IWAMOTO Naoki)
Orange Roof

in need of romance?
uncommon, sad, sweet