I don't really know how to explain it, but im looking for some romance manga where the characters' thought processes are explored in a lot of detail, so at points the characters will just sit there and the author will write their thoughts out with a lot of text. basically something with characters who are very introspective and take the time to process their emotions.

I can't really think of any good examples right now but maybe something like Koiiji? also I prefer shoujo or josei, but I'm fine with seinin as well!

You can try out Watashi no Shiawase na Kekkon, the manga or novel. I find the thoughts of both the female and male leads are explored.
It's still ongoing, so sorry if you wanted something complete.

I second this title and would also recommend Sakura-chan to Nozomi-kun.

You might try Say I Love You or Sand chronicles
They are both shojo.

Binetsu Kuukan
Sensei!

Octave if you can tolerate yuri.

Koi Kaze if you can tolerate incest.

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