Do I need help? Please give me some advice..?

Many of you, none like my parents and a few others, may think that I'm in a way.. "immature" to be tortured and bothered like this, but I am. It's been nearly four months since my girlfriend broke up with me. I took it seriously hard.. This wasn't some middle-high school "liking" one another. This is what my parents called "love" and I know so.. Because none like any other dates and such that I've been in, I can't shake this off. I've talked to a lot of people and they call say the same. They all say that I'll get over it. It's been four months and they are starting to say that I should have been over it long ago, but I haven't. My grades are going down from As and Bs to Ds and Fs. I don't see the point in trying anymore. I don't see the point in raising my grades and I don't see the point in living. I'm ashamed of how my life has turned out. I'm ashamed of how horrible things have gotten because of a mistake my ex-girlfriend and I've made. Now I'm miserable than I've ever thought possible. I can't stand it any longer.. Today, I sat where she and I saw our first sunset. I found a pebble and started to scratch myself on the arm. It just left a white mark behind. Then later, I don't know how to explain this, but I think I've gone insane and I felt no pain.. I started to cut myself five times or more. It doesn't hurt now and it didn't hurt before. It's barely bleeding too but.. I don't know. I don't know anything anymore. Please give me some advice.. I'm too ashamed to tell my parents anything. They have been through enough.. They think I'm over her and I'm not... I don't know what to do....