Totally unjustified contemplations of suicide

Hi, my name is Tom. In an attempt to try and get to grips with my mental well being i'm going to open up to this community, as I am too cowardly too open up to anyone in real life.

I am 20 years old and am currently studying a degree in aeronautical engineering at a good university in the north of England. . I come from a loving, supportive family and have never really been bullied to any extent. I dont perticulary hate my appearence, people have even said I was goodlooking, although when im down I sometimes pick my appearence as a reason for self hate.
I had one bad relationship when I was 14, (cheated on but i kept on going back to her) but I havd been with my current girlfriend for over 3 years and we are very happy together. I grew up all over the world due my father untill the age of 12 when my parents thought it best for me and my sister to attend high school in the uk. There i made many friends ( a few of which im still close with) and scored great grades at GCSE, I stayed on and did A levels too. These didnt go so well, I found myself to be incredibly unmotivated and as soon as I could drive I would simply go home rather than stay in lessons. In the end I had to re-do my final year there to attempt to scrape my way into uni, and so I did, allbeit with the same 'that'll do' attitude. Now im at uni I have made a good few friends and generally have a good time, we go out, drink and smoke a lot of cannabis but not at the same time, hell I even grew 3 of my own plants in my wardrobe! Despite me trying to turn over a new leaf, my old ways have crept back upon me and I have missed about 4 weeks of lectures now.

Onto the reason why im here. When I was in the afformentioned bad relationship, (age 14-16)I would get incredibly depressed around 'incidents' and I have a forearm full of scars to prove it, at this point I dont think I was thinking of suicide, rather just punishing myself as that is who I blamed. After this I dont recall having any problems. I then met my current girlfriend, about six months in she began to text flirt with another guy and I began to cut again rather than deal with it after she found out (about 2 months in)she begged me too stop and insisted they were only friends, and I believed her. She is still friends with that guy and once I relaxed things were fine and I havent cut since, other than when I failed my A levels and had to resit. I guess I realised that it was just a pathetic cry for help and didnt solve anything.

However I would prefer cutting to whats going on in my head now. I have always had random depressive mood swings lasting a matter of hours, sometimes resulting in cutting, but recently instead of cutting I have been contemplating suicide more so than ever before. When I get a swing I think about jumping infront of a bus, or infront a train If im out. Its occurring almost daily and im terrified that one day I may actually do it. When im
Around friends, im happy but it hardly takes anything to set me off and its hard to get out of a swing when it happens. Sometimes I even feel that its all put on, and that it is nothing more than me feeling sorry for myself and am craving the pity of others. Why can I get this sad all the time, when im just a middle class white boy whos been given every opportunity and has no reason to be.

I dont think I want to die, but I dont want to live like this.