I thought that Harry was like already so depressed and so low that he couldn't beat himself up too much more. Like he didn't have enough energy to do it. It was sad no matter what though. It'll probably be like he'll beat himself up about this particular incedent later on in the series. Thinking things like "I could have talked to him a few more times if I had only opened that package earlier...
" So once the initial shock of the death wears off he'll become more remorseful about what he did and didn't do with the last of his time with Sirius.
I say like a lot, lol, like, like, like-- I sound like a a valley girl, I should really cut back
also, sorry if this post sounds a little rambling. It's late and i'm tired *yawn*