Can someone help me sort out my head?

Seriously I think there's something wrong with me. I almost definitely have depression ( have since a year of bullying 3/4 years ago) and I can never get over things. For example, I broke up with my ex boyfriend of six months ago about a month ago. I know he's not feeling the pain like I do and I keep telling myself that but I just can't get over it. I actually genuinely do want to get over it but I can't. I rely constantly on other people's praise and when I don't get it the depression just gets worse. I actually don't have any friends at school, I'm by myself most of the time. I'm an underacheiver. I have a scholarship and I'm clever but I just don't seem to have the motivation to try. The only time I feel better is when I'm playing the guitar or planning my suicide (which I'm too cowardly to go through with). I used to enjoy life but now I barely have the motivation to get out of bed. Can someone please give me some advice as to A.) What's wrong with me? B.) How do I fix it?