The true depth of Snape's hatred for Sirius

[atrocity.geo]

No: HPFGUIDX 45325

I've been pondering this as of late, and thinking too much about 
it no doubt, but the hatred that lies between these two strikes me 
as deeper than Snape's anger about the werewolf incident and 
the Marauders' rulebreaking...and while discussing this with 
someone on the phone, my mom overheard me and asked what 
I was going on about...and I sort of blew her off saying "just 
debating why Sirius hates Severus, nothing big..." and mom's 
response was..."Oh, are they brothers?  Those sound like a pair 
of names from one family rather than 2 seperate names..."
At first I was rolling my eyes, then it struck me...what if, on some 
level...step siblings perhaps...Snape and Black WERE 
connected and theres some huge understory here that is just 
waiting to explode...then again, I could just be thinking about this 
too much as I just finished GOF on CD for the 3rd time.
Ah well...thoughts?

"atrocity.geo"