It's a great poem! The image of the candle is superb!
It's a simply beautiful poem, an expression of love affair based on mutual agreement and total commitment on both parties. 'My love feeds on your love, beloved' fully captures 'the give and take' relationship.
The poet persona deeply explores the vanity of life making references to the natural creation which will one day become 'pale.' A good reason human should live a good life before death beckons.