I have read it long time ago and now i wanted reread it but i have forgotten title. I tried search by genre and cathegories but....
Maybe somebody recognises it:

Girl starts in new school and is housed into school dormitory.

Her roommate is famous girl in school and outside school bc she is model.

One day girl discovers that her roomamate is actualy not she but he. To prevent leaking info she/he blackmails her to be silent.
There is many-many events but they fall in love a.s.o.

In the end she/he disapears but returns in day of her graduation, he is now he and looks handsome.
She runs after him and ...
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Who knows this manga? What is its title?

Sounds like Tenshi ja Nai!!

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Thanks it is it

( bows in amaze )