Riddle - He who holds the answer may enter

Question

Here's a riddle I used in a game some time ago. Not the best riddle ever, but we had fun solving it.

It was written on a translucent door, on the frame of which was written "He who holds the answer may enter". What's the riddle about and what would your action be?

We're quite the couple, you and I
If you let me live, I'll surely die

If you kill me to live another night
I'll be there next evening, at your side

I won't keep you warm, I'll give you that
And I am most cold when I wear my hat

Whenever I cry you just leave me be
while your tears are like poison to me

I see the pain in your eyes, whenever we touch
I shiver when you speak or shush

If we're too passionate you'll surely die
We're quite the couple, you and I

Answer 1

The item spoken of in the riddle is

a candle.

We're quite the couple, you and I
If you let me live, I'll surely die

Leave the candle burning, it will be consumed.

If you kill me to live another night
I'll be there next evening, at your side

snuff out the candle flame and you will be able to re-use the candle the next night.

I won't keep you warm, I'll give you that
And I am most cold when I wear my hat

Candle flames are good for (a little) light, not for keeping things warm; if you put a "hat" (a candle-snuffer) on a candle, it goes out and doesn't provide any warmth at all.

Whenever I cry you just leave me be
while your tears are like poison to me

The candle's "tears" are the wax runoff, which we don't do anything about; but our tears would put out the candle-flame.

I see the pain in your eyes, whenever we touch
I shiver when you speak or shush

it hurts us to touch the candleflame, and the flame flickers from the air-currents of our breathing or speaking.

If we're too passionate you'll surely die
We're quite the couple, you and I

Let the flame get too big/too close, you're in for a world of hurt.

So, my action would be

stepping through the doorframe while holding a lit candle.