The line in question is the second line in the second verse. I'd always understood it as "I'd give the stars and the sun 'fore I live," with the meaning that the singer/speaker would want to give the universe to the girl he loves before he'd allow himself to live and be with her. (In explaining this, I've realized that it actually doesn't make that much sense, but this reading persists for me just because it's the only one I had for so long.)
When I recently heard the Herman's Hermits version, I realized that the line break might not interrupt the meaning. Instead of two separate sentiments ("I'd give the stars and the sun 'fore I live" and "To thrill you with delight, I'd give you diamonds bright"), it's just one thought divided by the line break ("I'd give the stars and the sun for I live / To thrill you with delight") and then the shorter promise that "I'd give you diamonds bright." The "[be]fore" that I had thought was a temporal conjunction could be rendered as "for" and used as a causal conjunction. (It could be rephrased as "I'd give the stars and sun because I live to thrill you with delight.")
I suspect that the first of those readings ("I'd give the stars and the sun 'fore I live" as a distinct thought from "To thrill you with delight, I'd give you diamonds bright") made more sense to me because the same structure is present in the first verse: "I'd bring you diamond rings and things right to your door / To thrill you with delight, I'd give you diamonds bright." Because of the line break, it's read more obviously as the two promises "I'd bring you diamond rings and things right to your door" and "To thrill you with delight, I'd give you diamonds bright" rather than the uneven "I'd bring you diamond rings and things right to your door / To thrill you with delight" and "I'd give you diamond bright."
But if that weren't enough, when I transcribed the song, I found yet an-other reading. I'd been thinking of just the lead vocals, but in between those two lines, the backing vocals add "For your love." This addition multiplies the ways in which the lines can be understood.
In the first verse, there's now:
- I'd bring you diamond rings and things right to your door / To thrill you with delight, I'd give you diamonds bright
- I'd bring you diamond rings and things right to your door / To thrill you with delight; I'd give you diamonds bright
- I'd bring you diamond rings and things right to your door (For your love) / To thrill you with delight, I'd give you diamonds bright
And for the second verse:
- I'd give the stars and the sun 'fore I live / To thrill you with delight, I'd give you diamonds bright
- I'd give the stars and the sun for I live / To thrill you with delight; I'd give you diamonds bright
- I'd give the stars and the sun for I live (For your love) / To thrill you with delight, I'd give you diamonds bright
There are so many ways in which the words can be understood, yet they still mean more or less the same thing.