Well, even if it wasn't a messy break-up, it is still a not-so-minor life change on top of whatever chemical changes you've got going on inside you.

Don't obsess too much over the angry feeling - just go ahead and be angry. Write some rude, nasty latters and then rip them up and burn them. Buy some cheap yard-sale glassware, tie it in a grocery bag, and throw it down the stairs, just to have the satisfaction of hearing the sound of breaking glass (this is my personal favorite). Maybe if you just let yourself be angry you'll get past it.