The phrase "although I was alone" is correct and usable in written English.
It can be used to introduce a contrast or exception in a sentence, often to highlight a feeling or situation despite being alone.
Example: "Although I was alone, I felt a sense of peace and contentment in my solitude."
Alternatives: "even though I was by myself" or "despite being alone".
In one passage, Gornick describes being overcome, during an aimless visit to the Metropolitan Museum of Art, by a carving of a young Egyptian goddess: Although I am alone with the goddess, have no one to whom I could utter a sound, I nonetheless feel speechless: cannot find the words inside me to describe the engulfing emotion this little bit of wood and gold has aroused.
Sitting there one Sunday evening I was struck by two significant things: Although I was there alone, I did not feel either foolish or threatened.
Another example may be the population Hw, which is incompatible to other green populations although it is alone with the Tl population in the Green genetic clusters.
Sitting across the field, I watch from a distance and make notes – although I'm not alone, and I have been invited.
Although I am not alone in this, I don't have a lot of company.
It wasn't until later that I was finally able to put a finger on what it was about these people and their mission that did not sit well with me (although I am not alone with such feelings): nobody can do good development or aid work in a few weeks/months, especially not outsiders.
So when I got curious enough recently to google "why the singer Sia hides her face," I didn't bat an eyelash at her response (although I was tempted to stand up all alone in my casa to cheer her on).
Maybe I have spent too long in Lytham St Annes, and am turning into Peter Alliss, although I am sure I am not alone in finding what vestiges of political incorrectness the doyen of golf commentary has been allowed to retain quite bracing in the current climate.
I feel confident about the quality of medical care I will get in labour, although I am worried I'll be left alone.
In addition, Mr. Franco's recent appearances on the soap opera "General Hospital" as a handsome, enigmatic, platitude-spouting installation artist named Franco have earned him something of a cult following, although I can't be alone in feeling that their irony is outdone by their lameness.
