独身の友達とルームシェアしている。
I share an apartment with a single friend.
He is still single even in his thirties.
She has decided to stay single for her whole life.
He is leading a carefree single life in Tokyo.
既婚者 is the formal term for a married person, whereas 独身 is the everyday word meaning 'single' or 'unmarried', its practical opposite.
独身 describes marital status (being unmarried), whereas 一人暮らし describes the living arrangement of living alone regardless of marital status.
single person tax; bachelor tax
voluntary singlehood; singlehood by choice