DD and RAB

[prongs103]

No: HPFGUIDX 137545

I am utterly perplexed by the fact that DD's death and the escape of 
Snape bares no obvious fruit, since the horcrux which Harry and DD set 
out to find (consequently leaving the castle alone without dd's 
presence, allowing the death eaters in) turns out to be fake.  So DD 
poisoned himself and left the castle vulnerable ultimately leading to 
his death, for a FAKE horcrux? Cmon Mrs. Jo Rowling, WHY?  Someone 
please help me to understand this.  Also this RAB character, who is 
this?  It can't be anyone that is contact with DD b/c they would have 
told him of there discovery and actions.  This has been the biggest 
question on my mind since finishing the book, the other being, will 
Harry and Ginny end up together(I hope so)?

Sorry this post jumps around so much, I am new to the group. 

Prongs.