I can't even think of a good example. Maybe like Tasogare Otome Amnesia. It doesn't have to be about ghosts though. Or maybe Sankarea, though this one is too much of a comedy.

Sugar Dark - Umerareta Yami to Shoujo
Anorexia - Shikabane Hanako wa Kyoshokushou
Mushi to Medama to Teddy Bear

~4400 manga completed
~1700 ongoing...

Quite good if you can stomach all the creepy and disturbing things: The Voynich Hotel (ending kind of abrupt though)

Natsume Yuujinchou first one I thought about. Its not romance but if you havent seen it give it a chance.
The Pale Horse A bit slow paced and heavy on drama but it is what you are looking for I think.
Orange Marmalade recommend it. It is even completed 🙂
Pinocchio that one is a bit too sugary with no existence of creepiness .
Conductor a mystery, creepy, interesting and romantic in tragic way.
Shinrei Tantei Yakumo detective mystery with supernatural elements and a bit of romance.

Haru no Houtai Shoujo... Just finished it actually 😀

~4400 manga completed
~1700 ongoing...

Sekai Oni the sweet part only happens occasionally
And possibly American Ghost Jack
Also Subete ga Chotto Zutsu Yasahii Sekai but it's more weird than creepy...

I combined Horror + Romance + Supernatural to see what would happen and chose the Embalming - The Another Tale of Frankenstein series. Someone will bring up my reviewed Itoshi no Kana as it came to mind when i read the topic so i will do it.
You could also use Mystery instead of Horror for your search and consider Fantasy too.

I also read EU/US comics and am a librarian.
Manga-Masters, My ANN-Lists + Imdb