This is the 2942nd most frequent German word.
alleine
"Alone" or "by oneself."
In this sentence, 'alleine' is used as an adverb to indicate the subject is engaging in an activity without companions.
Ich gehe heute Abend alleine spazieren.
I am taking a walk alone this evening.
Here, 'alleine' conveys an emotional state of feeling isolated or lonely rather than a physical separation.
Er fühlt sich oft alleine, wenn er zu Hause ist.
He often feels lonely when he is at home.
In this case, 'alleine' emphasizes that the action was performed solely by the mentioned individual without help.