For me this song is about an almost relationship.

I'd like to say we gave it a try
I'd like to blame it all on life
Maybe we just weren't right, but that's a lie, that's a lie
(you tried to be with that person but you never became an official couple)

And we can deny it as much as we want
But in time our feelings will show
(and since a real relationship did not happen you try to deny that you had feelings for that person before because of your ego but if you see him/her again the same actions will show that you both had feelings for each other)

'Cause sooner or later
We'll wonder why we gave up
The truth is everyone knows
(You always end up wondering why you gave up on each other when you were almost there to having a real relationship.)

Almost, almost is never enough
(Almost relationships will never be enough because there will never be closure. It will never be enough because you can never get enough answers. There will always be what ifs and will always make you wonder why.)

So close to being in love
(so close to having a real relationship)

If I would have known that you wanted me
The way I wanted you
(You both have great feelings for each other but there was never a real relationship)

Then maybe we wouldn't be two worlds apart
But right here in each other's arms
(years later and you will see each other as strangers, you will still wonder the same question, but since you are already happy with someone else you'll wonder how would it have been if you became a real couple spending time with each other)

And we almost, we almost knew what love was
But almost is never enough
(Almost knew what it was like to be each other's gf/bf but it did not happen so you are only left with all of your imagination of being with him/her)

If I could change the world overnight
There'd be no such thing as goodbye
(Since it was an almost relationship there will be many regrets on how could you have done things differently to make it a real relationship)

You'd be standing right where you were
And we'd get the chance we deserve
(If you could have done things differently in the past, you know you will make it right and have that chance to be with that person)