for a long time
私は長いあいだ彼女を愛してきた。
I have loved her for a long time.
ずっと長いあいだ、誰も来ていない。
No one has come here in a very long time.
彼らは大の親友で、長いあいだ離れ離れになっていたのだ。
They were the best of friends, and they’d been apart for a long time.
彼がそんなに長いあいだ病気だったとは。
I had no idea he'd been ill for so long.
彼は長いあいだ病気です。
He has been sick for a long time.