I won't be a hypocrite and say the moment will pass. I'm 16 now and have dealt with 'this' kind of pain since I was 11-15. I try not to tell many people about it because it gives off a completely different vibe/impression about me. I've become very optimistic since my past because of:
1.) music: it gives this sense of relief, a break from life. the thoughts subside a little when you lay in bed, close your eyes, and it's just you and music.
2.) poetry: rather than acting out your thoughts, write it out. words can be so much easier than actions.
3.) friends and family: I suppose for you, imagine how your granny would feel if she found out you left the world. imagine how your friends would feel. if possible, seek help. talk to someone close about this.
4.) the thought about the 'ripple effect' : once you think these thoughts and do something bad, it's like a ripple in a water. it goes to everyone around you, affecting them all. then it affects everyone close to them, etc. not a great process really...
5.) the thought of LIFE: there's so much in life that you haven't experienced. think about how all the possibilities and joyous times in your future have been taken away because of a 'spur of the moment' type of thing.
I apologize if I made this very long and kind of.. lecturish. But I suppose it's because from personal experience I find suicide or thoughts of suicide to be a bigger deal than it is.
we, interferencers, have got the words to reassure you, but YOU have the choice to make things better or worse.
I really hope things get better for you, and just know that there's so much happiness out there for you to feel
please keep us updated on how things are going for you