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not writing or contacting for a while; neglecting to write (call, visit, etc.); failing to write (call, visit, etc.); long silence
長い間不沙汰をしていて申し訳ありません。
I'm sorry for not being in touch for so long.
不沙汰が続いたので近況報告の手紙を書いた。
I'd been out of touch, so I wrote a letter updating my news.
不沙汰をお詫びして久しぶりに電話した。
I apologized for being out of touch and called after a long time.