I think that the song is basically about someone who is completely estranged from their former love, and it just seems so hard to believe that they were together. Now that he thinks back, and the only thing he can have to prove that it happened was "A photograph of you and I...In love...".
To me this song means: Is everything we had a dream. I have photographs to prove we were together but the memories are fading. Yea i admit to be selfish, but i am not the only one. So you I have to forget and say goodbye to forever, this is the way it must be.