Sing to the music of Let Her Go, originally by Passenger.

You can listen to the original song here: Let Her Go.

Well, you only need the light when it's burning low
Only miss the sun when it starts to snow
Only know you love her when you let her go

Only know you've been high when you're feeling low
Only hate the road when you’re missin' home
Only know you love her when you let her go
And you let her go

Staring at the bottom of your glass
Hoping one day you'll make a dream last
But dreams come slow and they go so fast

You see her when you close your eyes
Maybe one day you'll understand why
Everything you touch surely dies

But you only need the light when it's burning low
Only miss the sun when it starts to snow
Only know you love her when you let her go

Only know you've been high when you're feeling low
Only hate the road when you're missin' home
Only know you love her when you let her go

Staring at the ceiling in the dark
Same old empty feeling in your heart
'Cause love comes slow and it goes so fast

Well you see her when you fall asleep
But never to touch and never to keep
'Cause you loved her too much
And you dived too deep

Well you only need the light when it's burning low
Only miss the sun when it starts to snow
Only know you love her when you let her go

Only know you've been high when you're feeling low
Only hate the road when you're missin' home
Only know you love her when you let her go

And you let her go (oh, oh, ooh)
And you let her go (oh, oh, ooh)
Well you let her go

'Cause you only need the light when it's burning low
Only miss the sun when it starts to snow
Only know you love her when you let her go

Only know you've been high when you're feeling low
Only hate the road when you're missin' home
Only know you love her when you let her go

'Cause you only need the light when it's burning low
Only miss the sun when it starts to snow
Only know you love her when you let her go

Only know you've been high when you're feeling low
Only hate the road when you're missin' home
Only know you love her when you let her go

And you let her go.

BURNING LOW= If a fire is burning low, the flames are low, so it’s a small fire, giving out little light and warmth.

LET HER= The “perfect” British pronunciation would be /let hɜ:*/ but the pronoun HER is often pronounced without H so we say /ɜ:*/or /ə*/. There is a rule that works in standard AmE and in conversational BrE which says that when a T goes between vowels it sounds like a quick D (similar to the R in the Spanish or Italian word “cara”). In BrE the /r/sound disappears when not followed by a vowel, so the result of it all is the pronunciation you hear in this song: /leʀə/ (the same as "letter" in conversational BrE).
LET HER GO= If you let her go, she leaves you and you don’t do anything to stop her.

HIGH= (coll.) If you are high you feel very very happy.

LOW= If you are low or feel low you are sad or depressed.

AND YOU LET HER GO= The verb LET is irregular (let – let – let ) so it can be present or past tense. In the sentence “When you let her go” it is a present tense (in this case = if you let her go). But in the sentence “And you let her go” it is a past tense. So what he says is that if you let your lover go, you’ll miss her… and you have let her go, so know you know how much you loved her for real.

AND YOU= Assimilation rule number 2: D + Y = J  /ændʒu:/ or /əndʒə/ 

STARE= /steə*/ If you stare at someone or something, you look at them intensely for some time (or for a long time). If you stare at the bottom of your glass, you are drinking alcohol (to forget how sad you feel) but you are thinking of her, so your eyes are fixed on the bottom of your glass while your mind is fixed on her memory.

LAST= If something lasts, it has a duration. If a movie lasts 2 hours, that’s the time you need to see the whole movie.

SURELY= /ʃɔ:lɪ/ In a certain way, without doubt, for sure.

BUT YOU= Assimilation rule number 1: T + Y = CH /bətʃu:/ 

HEART= /hɑ:*t/

NEVER TO TOUCH AND NEVER TO KEEP= If she is never to touch, that means that it is impossible to touch her now or in the future. To keep is to have with you, the opposite of “to lose”.

DIVE= To dive is to swim under water; also to jump head first into the water. If you dive too deep into something (metaphorically) you are too involved or interested in it.

This song is about a man whose heart is broken because his lover left him. The song is actually a monologue to himself, so the “you” in the song is really an “I”. His lover left him and he blames himself, she didn’t leave, he let her go, and the idea is haunting him and torturing him (he repeats it over and over again).

It is now that she left, when he finally fully appreciates everything that she meant for him, and he expresses this feeling of lost and regret making different comparisons:

Well, you only need the light when it's burning low
Only miss the sun when it starts to snow
Only know you've been high when you're feeling low
Only hate the road when you’re missin' home

But what he is really talking about all the time is:

Only know you love her when you let her go

And then again, his self-accusation. She just didn’t leave, it is him that did things wrong and so it was him who lost her:

And you let her go

She left not long ago, we can see that because of the use of the present perfect (recent past) in the sentence:

Only know you've been high when you're feeling low

So now he feels heart-broken and he started to drink to forget. But deep in his thoughts, when he finishes his last glass of whisky (or whatever) he remains there motionless, oblivious of the whole world outside:

Staring at the bottom of your glass

And what is he thinking about? He is just wishing he could have a relationship that would last, so we assume he had many other relationships and they all ended badly because of him:

Hoping one day you'll make a dream last
But dreams come slow and they go so fast

He is once again blaming himself for the loss, and he does that because it’s always the same problem, he can’t make a relationship last and they leave him. The problem is that he knows that he’s doing something wrong, but he doesn’t know what it is, why he spoils everything:

Maybe one day you'll understand why
Everything you touch surely dies

So this is a broken relationship in a line of many other broken relationships before; he knows this feeling of loss very well, it’s not the first time:

Same old empty feeling in your heart

Still, he starts every relationship with all the enthusiasm of the first time:

'Cause you loved her too much
And you dived too deep

So basically, this is a song of a romantic man deep in sorrow who is just wondering why he can never find his true love... and keep it.

Mike Rosenberg explained the song's meaning: "In my mind the song has two meanings"; he said, "the first is quite literal as I wrote it after a break up and it is about letting her go. But then there is a bigger idea going on and is more about not really understanding and knowing what you have until it is gone and I think everyone can definitely relate to."

One of the things we humans do is habituate; we become used to things that are just there. The end result of this kind of habituation is that we tend to take for granted the things that we have and it does not mean that we'll miss it when it's gone. After all, getting used to something doesn't mean that we won't miss it terribly when it's gone.