I've seen a few series like this. A hero is in love with a heroine (or vice versa), but the two of them due to various circumstances are trapped under one roof. Not only does this cohabitation lead to interaction and exposure that both parties weren't prepared for, but it raises implications concerning any attempts at romance. A perfect example of this is Pastel.

In this series, hero Mugi, just dumped by his girlfriend, meets a girl named Yuu on vacation and is absolutely smitten by her. But before he can find a way to apologize for certain actions and ask how to see her again, she takes off. He heads home despondent only to find Yuu in his bath at home. It turns out their parents were best friends and his dad promised to take care of Yuu and her sister if anything happened. Thus, the two girls who just lost their father are moving in, and since Mugi's dad's always gone it's just the three of them. Every day Mugi finds himself falling more in love with Yuu, but Yuu has nowhere else to go, and Mugi would never make her only home an awkward place to live in, so he desperately keeps quiet about his feelings.

Most step-siblings/incest manga are like that. One that I recently read is Momoyama Kyodai.

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Shoujo & Romance Manga Lover || Cleaner-Typesetter

Try:

Parallel
Ai Yori Aoshi
Crossroad
Desire Climax
Gekkoh
Living Game
Love Hina
Milk Crown
Orange Yane no Chiisana Ie
Private Prince
Suzuka
Tokyo Crazy Paradise

Not all of these match perfectly, but they all have the cohabitation theme front and center.

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