I read somewhere before that brain edits memories, changing and updating the past with new information. I think that emotions you experience throughout time when you remember particular memories - change. You may feel sad at the beginning, but then think "It was a useful lesson" or "I was happy at that time". Or maybe there are happy memories that later make you feel sad or hurt. And after years you won't remember as much details about these memories, that's because you've made new ones.
Time tends to erase many things. You meet new people and make new memories with them.
Memories are like drawings - as time goes by you may edit them by ereasing some parts or make them fade away by drawing over the old memories with new/better ones. It's best to not sink in memories, but get something useful out of them.
