I'm sure you feel a lot of pain and find it difficult to cope with. I guess you feel your life is scrambling down and you can't see any way out.
But there will be a way out, I promess it. Your pain will slowly go away with time. Time is always the best cure for broken hearts. You must be patient, obviously you will not forget your lover over a week or so. But you must believe that days after days you will feel better. I know what it is to get up in the morning and go to bed in the evening with this huge weight over your chest. But this weight will get lighter and lighter. One day you’ll wake up and the weight will be gone.
I don't want to scare you but you'll have other break ups in your life. Love is never eternal unlike diamonds. People who stay together for so long have learnt to take their relationship to another level and don't rely only on feelings.
About whose fault it was. It is nobody's fault. I'm sure you haven't done anything wrong nor did your lover. Sometimes weariness is to be blamed. The most difficult thing to do is to accept that your relationship wasn't as fulfilling for each other as it could have been. Sometimes the break up happens just after a silly incident, but it is only a trigger. It means the relationship wasn't strong enough to get over this kind of little incidents.
Now, you must react as an adult (even if it is difficult to keep your mind clear). You were old enough to fall in love, you must now be old enough to react like a sensible person. You must understand that hurting yourself won’t get your lover back. You must understand that destroying yourself won’t make you feel better either.
Last thing, you’re 13, you have many years yet to live and you will meet another lover. I know you might not want to hear this but it is only the truth. When I divorced at 28, I thought I was going to stay on my own for the rest of my life. A year and half later I was falling in love for a girl like it never happened before. It took me a year or two to get emotionally through my divorce but once I was ready to meet someone else I found out that my life was far from being over. Today I’ve split with this girl I fell madly in love with. Again it took me at least a year to get through it but now my experience tells me it is just a matter of time for the pain to vanish.
Your love life will be full of great and no so great moments. If you don’t have bad times in your life how do you want to enjoy the good ones?
Take care and respect yourself.