Actually, tormenting Snape was James' idea as well ("Because he exists" comes to mind), and in OOtP Sirius said that James hexed Snape all the time in seventh year and hid it from Lily.

But it would have been nice if Sirius had regretted trying to kill Snape, instead of regretting not finishing the job (and trying to do so in PoA). You'll notice he doesn't admit to scraping Snape's head into the wall in this apology.

Anyway, this is a good AU, and it would have been nice to see _both_ of them this mature.

this was great

An excellent example of the fact that people grow up and sometimes regret their actions. Keep writing

I like it! I would like to think that Sirius is mature enough to take an objective look at his own and others' behavior. Nicely done!

Good job!