What is the meaning of “half as dear and precious to each other as” in this?

Question

'To be to you what you were once to him,' cried the younger, falling on his knee before him; 'to repay your old affection, brother dear, by constant care, solicitude, and love; to be, at your right hand, what he has never ceased to be when oceans rolled between us; to call to witness his unchanging truth and mindfulness of bygone days, whole years of desolation. Give me but one word of recognition, brother—and never—no never, in the brightest moment of our youngest days, when, poor silly boys, we thought to pass our lives together—have we been half as dear and precious to each other as we shall be from this time hence!

Dickens : The Old Curiosity Shop

Answer 1

The clause is parsed wrongly in the question. It is:

{[never] have we been half as dear and precious to each other} {as we shall be from this time hence.}

It is a straightforward as... as comparison.

Compare

"The water in the river has never been as high as it is now."

Answer 2

The meaning of the phrase may be understood by attributing a word omission to it.

To take a simpler example:
The light has never shone half as brightly as it does now.
This is not a plain statement that the light was always darker or lighter than 50% of its present brilliance.

With the omitted words inserted, the meaning is:
The light has never shone {even, or as much as} half as brightly as it does now.

Furthermore, the reader is invited (by understanding the conventional usage) to consider a scale of brightness that extends from zero upwards without limit. The implication is that the light has always been less than half of its present brilliance, rather than more than half.

In your quotation, the implication is that the brothers have never loved each other as much as half the present, and that henceforth they will love each other more than the present.

In truth, the author’s usage is qualitative and figurative, for who can measure love? So the real meaning is that the brothers will love each other more in the future than they did in the past.