by (or British on) one's lonesome
informal All alone: I’ll be by my lonesome all night...- That is less than the equivalent would cost you for eating the same on your lonesome in Paris or New York.
- What am I gonna do in a van all on my lonesome, huh?
- I've lived on my lonesome for abut 5 months now and have realised that there are a number of things which need to be discussed.
See parent entry: lonesome