on one's lonesome
Alone; without aid or accompaniment.
"Sittin' there all on her lonesome the whole day long, it's understandable she gets down in the dumps."
adj
Unhappy due to being alone; lonely.
'Where'er the sun shakes out his spears, and the lonesome waters mirror up the moon, where'er storms roll [...] there shall thy power pass and thy dominion find a home.'
noun
Oneself alone.
I sat and watched the cars pass all by my lonesome.