Ling led Orient into League One following a dramatic final-day win over Oxford United in 2005/06, when Lee Steele scored the stoppage-time winner that clinched their promotion.
He had been the sixth longest-serving of the 92 Premier and Football League managers.
After Saturday's match, he told BBC London 94.9: "We will find any way we can to lose a game at the moment.
"It's like a death wish - how can we chuck this game away? You've got to dig deep because it hurts.
"It hurts the lads in there and it's hurting me at the moment - we do see to throw away a winning position at the drop of a hat."
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