To answer the official question, in every sentence (not every clause, but every sentence) the first verb in the main verb phrase must be one of
- a Present tense form (am, is, are, have, has, does, do, or
Verb + -Z₃, the 3SgPr inflection)
- a Past tense form (was, were, had, did, or
Verb + -ED, the Past inflection)
- a Modal auxiliary verb (can, could, may, might, will, would, shall, should, must)
English modal auxiliaries are not inflected for tense, so they are either not in any tense or they are always present tense, depending on what kind of theory of tense you're applying.
So either all English sentences are in a tense, or there are some that aren't. But that's just how one describes the language -- it doesn't affect the grammar.
Time in English is frequently indicated by tense, but often enough it's also -- or even only -- a matter of the words or constructions used. See the Deixis Lectures for more on expressions of Time.
English tensed verb forms, however, often specifically don't refer to time. For instance, the Present tense, when used with an active verb, is most likely to refer to an habitual occurrence than to the present time. E.g,
- Bill walks to school means he walks (almost) every time he goes to school.
- That dog bites means that the dog has been known to bite people on some occasion(s).
- Mary drives a Toyota means that Mary usually drives (and probably owns) a Toyota.
None of these refer to what Bill, the dog, or Mary are doing at the present time -- neither the time of speaking nor the "present" of a narrative. This is called a generic construction.
The particular use in the original question licenses the use of a past verb form to indicate an unreal supposition, much the way certain regular subjunctive verb endings do in European languages; but only sporadically -- not regularly. This counterfactual conditional construction, like most archaic remnants, is idiomatic, and governed by only a few constructions and verbs. So one finds
- I wish I were home now.
- If I were you, ...
- If I had the money now, I'd give it to you.
The past perfect is necessary when the sequence of past events may otherwise be unclear. Compare:
She cooked dinner when I arrived.
She had cooked dinner when I arrived.
However, it is certainly not 'very necessary' to use the past perfect in OP's context. Ten years ago is ten years ago whether from the perspective of today or yesterday. There is no ambiguity of sequence.
It is somewhat different if the speaker is reporting a meeting with his girlfriend at a more remote point in time:
In 2009 I met my first girlfriend in Paris. She was as beautiful then
as she had been ten years before.
Here we do have a clear 'past in the past' so the past perfect is unproblematic. As to whether it is necessary, I see no significant objection to the past simple here too:
In 2009 I met my first girlfriend in Paris. She was as beautiful then
as she was ten years before.
[Note that replacing before with ago in the above sentence changes the meaning.]
Best Answer
Farlex gives this (common) usage for headed; though this is the adjectival usage, the participle usage corresponds:
The present participle is certainly not a wrong alternative (as an adjective or participle), and is, as you imply, at least as logical. The fact that 'head' can be (and 'head out' virtually has to be) punctive (then, we headed west / we headed into the wind // we headed out west) as well as durative (we headed steadily west / we were heading into the wind) very probably gives rise to the choice. Between, I'd say, "So, where are we headed?" and "So, where are we heading?"
Google Ngrams show that the 'headed' version ('where are we headed') has been consistently appreciably more popular in the US since say 1985; in the UK, until about 1980, it was the other way round. The versions are now roughly equal in popularity in the UK, possibly because of the influence of American film dialogues ('headed' sounding more butch).