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Он давно жил там = He lived there a long time ago.
Он долго жил там = He lived there for a long time.

Ya got it :)
(Except the last one).

Долго = long time
Давно = long time ago

1) Мы давно не виделись
2) Мы долго не виделись
We haven't seen each other for a long time.
They both mean the same, maybe slight shade of "in ages" in...