I'm feeling like a failure

I've been working my ass off lately and it hasn't paid off as well as I hoped. I've been studying like crazy, spending days at a time at the library reading, making notes, going over slides, writing essays, and then I ended up with F, C-, B-, B-, B-, B. That wasn't the plan. I worked my ass off and I still failed. It kills me. I put in everything in me, i put in so much effort, I worked my ass off and I still didn't do well. That's what hurts. It just makes me feel like I'm an idiot. I mean who puts in so much effort and then fucks up... only someone who's stupid right? A failure. If I hadn't put in all the effort, I wouldn't care as much, but the fact that I did and I still couldn't get As, hell I couldn't even PASS all my courses! WTF is wrong with me? Why am I like this? My parents were smart, my siblings are smart, why am I the idiot that can't seem to do shit right?
It's May 2014. This was supposed to be the time I'd be graduating university. All my friends are sending me photos and posting stuff on Facebook and all that of them in their graduation gowns, graduating, getting their degrees and moving forward in their lives and I'm sitting here at the library once again with another 18 courses to go. I'm happy for them, they've worked hard for it and they deserve them obviously, but is it wrong to be jealous of them?