by yourself

by (one)self

1. Alone. Because there's usually so much going on with the kids, I really enjoy spending a quiet Saturday night by myself.
2. Through one's own efforts alone. You can't move that table all by yourself! Here, let me help you. My little girl loves to get dressed by herself, so tutus and cowboy boots have become the norm around here.

by yourself

 
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.