All by (one's) lonesome American British informal
Used to refer to someone who is entirely alone, without anyone else.
I'm sitting on the balcony all by my lonesome.
Jack has lunch all by his lonesome at the cantina after breaking up with his girlfriend.
My roommate returned to his hometown, so I have been at the dorm all by my lonesome for 2 months.
Used to say someone is alone
Without help or support from others
Be on one's own.
Isolated, lonely, or abandoned
To live alone as a bachelor
It was often said by a photographer when he would like small children to look at the camera and smile before he took a photo.
When the photographer said “watch the birdie”, all of us looked at the camera and smiled.