Duration + 没 + Verb + 了 (how long you haven't …)

How long it's been

• Easy: "I studied for ten years" — 学了xué le十年shí nián.
• Tricky: "I haven't studied in ten years." The word order flips.
• The time of absence jumps in front of the verb.

Duration + not / haven't没méi + Verb + (completed / change)了le

• Pattern: (already已经yǐ jīng +) Duration + not / haven't没méi + Verb + (completed / change)了le.

we我们wǒ menalready已经yǐ jīngten years十年shí niánhaven't没méimet见jiàn了le。

• 十年shí nián没见méi jiàn(completed / change)了le = "haven't met in ten years (and counting)."

Mirror image

• "Have done X for a time" → time after the verb: to see看kàn(completed / change)了le十年shí nián.
• "Haven't done X for a time" → time before the verb: 十年shí nián没看méi kàn(completed / change)了le.

Recap

Read the full reference: HSK 3 grammar — Adverbs.