I'm sorry to hear that Tom...
Mine is Fix You: Coldplay.
I went into a sorft of bad place last year... I stayed in my house, in my room... all the time. I ignored all the people I was close with. But I listenend to that song religiously... It helped me realise who my real friends were and that this person was always with me... no matter what anyone says.
Thats all the reminiscing I'm doing... :P