If you liked the Hirunaka no Ryuusei manga, the Anime-Planet community thinks you'd like:
When Fumino Kaji’s parents died, she and her young brother, Teppei, were ferried from relative to relative. One day when they're finally fed up of being passed around, the pair decide to run away from home. Alone in the world, help arrives from the most unexpected source, Fumino's English teacher, Kazuma, who offers to take them in. Not believing that he means to commit to the idea, Fumino jokingly agrees to the idea but only if he will take her in as his wife and much to her surprise he agrees! Now the three live together with Fumino and Kazuma acting as man and wife in name only, but after falling for each other, the pair must try to act normally at school to ensure that no one discovers their secret.