Just add a was or is after the date.
Practically speaking, it doesn't really matter which one you use.
Either one will work equally fine: August 22
nd , 2012 was the day my life changed forever and
the day I met you.
The sentence would actually sound a lot smoother if you rewrite it like this: August 22
nd , 2012 is the day when my life changed forever because it was the day when I met you.
You can make it even shorter: August 22
nd , 2012 changed my life forever because it was the day I met you.
Or shorter still with the day I met you as a parenthetical statement: August 22
nd , 2012—the day I met you—
changed my life forever.
ell.stackexchange.com/users/6450/Michael Rybkin
You could start the sentence with the preposition on On August 22, 2012, my life changed forever when I met you for the first time .
ell.stackexchange.com/users/1694/Mari-Lou A
Like @Bilkokuya, I too find the current wording is essentially best, I would just change the punctuation slightly (and remove a word).
I would switch the first second comma for a colon, and change the word 'and' into an hyphen m-dash (or n-dash if you're a rebel).
Spaces should be removed from around your dash (but it looks ugly so be even more rebellious and leave them in if you feel like it).
August 22, 2012: the day my life changed forever – the day I met you.
As Bilkokuya says 'Any other phrasing makes it sound like a story, and loses the significance.'
ell.stackexchange.com/users/89/mcalex
As others have said, leave the words and change the punctuation.
August 22, 2012—­the day my life changed forever, the day I met you.
But if you need a true sentence (requiring a verb) rather than a phrase, how about, August 22, 2012 was the day my life changed forever—the day I met you.
This is perhaps more a style question than a usage one.
For me, putting a coordinating conjunction like and before "the day I met you" weakens it compared to the original phrasing.
I think there should be a progression "August 22, 2012"
[mundane], "the day my life changed forever" [special], and finally "the day I met you"
[incomparable].
Note:
This answer assumes that the reason your life changed forever on that date was because of meeting this person.
ell.stackexchange.com/users/19943/Gossar
You can use several different approaches.
You could insert the verb after the date.
(1)
You could paraphrase the sentence.
(2)
You could use a preposition before the date.
(3) August 22
nd , 2012, was the day when my life changed forever and the day I met you.
22
nd of August, 2012, changed my life forever because it was then that I met you.
On 22 August 2012
my life changed forever because I met you that day.
You could use this style guide to help you.
You could rephrase it like this: It was the year 2012, the 22 nd of August when my life changed forever because I met you.
ell.stackexchange.com/users/44134/SovereignSun
It depends - most would agree that your sentence is not strictly grammatical with out a main verb.
But semantically, the sentence works quite well, and delivers a strong declarative statement about the date as a subject (it's all subject) and its personal importance to the writer.
This form, used prudently, is generally acceptable for informal language, and is a matter of style and emphasis, but it is generally unacceptable, for formal use in particular, not to have a main verb.
So as a matter of style, it is a dramatic way to introduce a subject.
I would point out that the original does not make it clear that the reason the writer's life changed forever on that day is because someone was met on that day.
It could just be a coincidence.
The meaning is a bit vague or ambiguous in this regard, which isn't a bad thing.
The following, somewhat reduced, has a similar feel, is grammatical and perhaps a bit less ambiguous, but is not as dramatic.
August 22, 2012, the day I met you, my life changed forever.
a version of: The day I met you, August 22, 2012, my life changed forever.
a version of: My life changed forever on August 22, 2012, the day I met you.
Certainly, August 22, 2012, the day I met you, the day my life changed forever, is a fine way to begin a story about that day.
Yes, it presents a grammar issue
but it's not serious if it is done intentionally (and infrequently), and there's nothing inherently wrong with ambiguity
- these are devices for writers, some things are better left open-ended and then unpacked in the telling of a story.
ell.stackexchange.com/users/57453/Ubu English
I want to say:   August 22, 2012, the day my life changed forever and the day I met you.   My only problem is that I don't know how to start a sentence with a date. If someone could help me with this that would be great thanks.
How do I start a sentence with a date?
ell.stackexchange.com
<grammar><conjunctions><questions><time><dates>
ell.stackexchange.com/questions/154375
ell.stackexchange.com/users/68613/Leah
You could insert the verb after the date, you could paraphrase the sentence, or you could use a preposition before the date.  For example: August 22nd, 2012, was the day when my life changed forever and the day I met you", "22nd  of August, 2012, changed my life forever because it was then that I met you", "On 22 August 2012 my life changed forever because I met you that day", or " It was the year 2012, the 22 nd  of August when my life changed forever because I met you". You can use several different approaches. 
You can use several different approaches. You could insert the verb after the date.   You could paraphrase the sentence.   You could paraphrase the sentence.  