wǒ zài wàimiàn děng le hěn jiǔ.

Here 在 introduces a location phrase: 在外面 = “at/outside.” It modifies the main verb 等.

• Location use: 我在外面等了很久。
• Progressive “be doing” is expressed with 正在 before the verb: 我正在外面等。
  You don’t say 我在外面在等. If you want both location and progressive, use 我正在外面等 (or put 正在 after the location: 我在外面正在等).

This 了 is perfective aspect, marking the action as bounded/complete, not a “past tense.” 等了很久 = the waiting lasted a long time (as a completed stretch).

• Completed duration: 等了很久
• Habitual/future prediction: 要/会等很久 (no 了)
• Negative for past/completed: 没等很久 (use 没; don’t use 不 here, and don’t put 了 after 没).

Duration normally follows the verb (often after 了): 等了很久.

• For an ongoing situation now: 等很久了 (duration before the sentence-final 了).
• Bare 等很久 is fine with modals or in non-completed contexts (e.g., 要等很久), but for a completed past stretch you typically say 等了很久.

In modern speech, 久 is usually modified by a degree word; 很久 sounds natural and neutral. Bare 久 after a verb is rare/very formal. Common alternatives:

• 好久 (colloquial, a bit more emotive)
• 很长时间 (more literal)
• 半天 (colloquial “a long while,” not literally half a day)

Several natural options:

• 我在外面等你等了很久。 (V + O + V + 了 + duration)
• 我在外面等了你很久。 (also common in speech)
  Avoid 我在外面等很久你 (wrong). If the object is the topic: 你，我在外面等了很久。

Put the duration after the verb (often after 了):

• 我在外面等了两个小时。
• Ongoing up to now: 我在外面等了两个小时了。

That’s usually incomplete. With perfective 了, Chinese prefers a complement (duration, result, object, etc.):

• 我等了很久。
• 我等到了他。 (result: “managed to wait until he arrived”)

Canonical order is Time > Place > Action:

• 我昨天在外面等了很久。
  Other time words follow the same rule: 我刚才/那天在外面等了很久。