4 Flights of Stairs on the Right(1950)

Dr. Jürgen Wenter and the pretty Marianne Müller are both looking for a room. They both come across the same advertisement: "2 furnished rooms for rent." Since neither wants to back down, they view the apartment together. It belongs to old Mr. Döhring, who insists on renting only to a married couple. So they pretend to be one. Jürgen sees no danger in this, as he is already engaged to Dagmar Prinz. Both of them intend to drive the other out as quickly as possible anyway. The petty squabble goes well until a friend finds Marianne more than just nice, and Mr. Wenter realizes he is jealous. A huge fight ensues, which ends with the two falling in love. But with the help of old Mr. Döhring, the complications continue for quite some time. Finally, after an embarrassing confession from the old man, the two become a "real" married couple.