The stalker came again and rang the bell at the house door for a long time. I sat silently at my desk in case someone let him in and he came to the apartment door. Someone asked him what he wanted from a window; I heard him explaining; they didn't buzz him in. He went back to ringing the doorbell. After a while he stopped. I assume he has gone away. I do need to leave Berlin.
It seems to me that life would be impossible if one went around anxiously wondering whether it was safe to let people know where one lived, but this is pretty tiring.