By yourself - Idioms by The Free Dictionary
1. with no one else present; alone. Do you want to sit here by yourself, or can I sit here too? Don't sit at home by yourself. Come to the movie with me.
2. with the help of no one else. Can you really do all this cooking by yourself? Bill, can you lift this box by yourself?
References in classic literature
How long do you want to be left by yourself
in the house?
And they'll all look like they're fairly mature, which will make you feel a lot better about being the 30-something dude drinking beer by yourself