for a long time
prep. phr..prep. phr.. This phrase means something happens or continues for many hours, days, weeks, or years.
prep. phr.. An adverbial prepositional phrase indicating a significant or extended duration of time.
We have lived here for a long time.
She stared at the painting for a long time, trying to understand its meaning.
The kingdom had been at peace for a long time, so its people were unprepared for the sudden invasion from the north.
Often used with the present perfect or past simple tense to describe a duration.
Contrast with 'since', which marks a starting point (e.g., 'since 2010'), whereas 'for' marks a duration (e.g., 'for ten years').
I know him for a long time.I have known him for a long time.Use the present perfect for states that started in the past and continue to the present.