I could have written both your recent posts Dobbs and I'm going through pretty much exactly the same thing.
I got an essay back that I actually got a worse mark for than yours (and I'm a third year) and although I knew it was poor I never expected to get the mark that I did. My real problem though has been the second essay I got back. I put weeks of solid effort into it (more probably than I've ever put into any essay), I read more than ever, I drafted and redrafted it and none of it was written the night before. And I ended up with a worse mark than I've had for essays read and written pretty much in 24 hours. So I now can't see the point of trying if I'm going to do terribly anyway. I've not been feeling good about being here for a while and so I set myself a minimum grade that if I didn't get for this essay I'd leave but I set a target so low I thought I'd easily get over. And I didn't. It's shaken me so much.
Hope things get better for you.