I can't sleep thinking about something

Because of something on my head I just cannot sleep. I was a bit sleepy about 10.30PM but then when I come to my room and listening for this one particular song it reminds me about the whole thing in my head. It was something sad and something that I never expected would happen. But it had happened and it stays on my mind most of the time. I have tried to forget it but it went temporary and when I'm listening to a sad song it comes straight to my head. Sometimes, no matter how tired I am or how busy I am it always appear on my mind. Sometimes I feel guilty and sometimes it makes me think that I am a selfish person. I remember every single moment just before I left the person in the airport. I remember the tears and I remember the last call before the plane took off. Everything changed when I came to the UK in 2009. Anyway, every people has memories and the best usually stay longer. Some people say we don't have to forget all the memories with someone to forget someone because the memories are like colours that colouring  your life. Which is true indeed but the thing is, we don't need every colour! Huh...I am tired I need a rest now......