Timetofly hits on one of the things I struggle with a this point. Even happy memories can become sad ones now because you know what happens in the future. Those memories are tainted. You can still look back and say that was a good day but in the shadow is this sadness.
Yep, some things (dates, places, events, etc) are forever changed. For some of these, ongoing healing will allow you to hold on to grace when you feel the sting of painful reminders. But some things you can choose to let go of (stop certain events, change places, etc) and some things you may choose to reclaim in a different way.
I worked with a wife who struggled with all the places her husband had taken his affair partner. Things that had belonged to the marriage were now soiled with the awareness that "they" had used them as well.
In some cases, she just chose not to go there anymore and choose new places to make their own. But there was one place -- a hill that overlooked a town -- that was difficult to get over because they had to pass it every time they visited his family. She would get anxious and physically sick every time she knew they would be going there.
She worked to prepare her "reclaiming" of this place. On their next trip, she asked her husband to drive to the overlook. She had already written out every ugly thing the affair had done to that place (known affair encounters, imagined images and conversations, the feeling of something precious being ripped away from her and handed to another woman) on pieced of paper.
The parked on top of the hill. Together, they sat in the car as she recounted the dark thoughts and feelings to her husband. Then, she got out of the car, dug a hole on the hill and buried the written testimony of pain. On that spot, they each collected stones and built a little monument of their commitment to each other.
Did this act change history? No.
Did it make her forget the pain? No.
But it allowed her to begin taking control of her story. And as they drive past that place now, the last memory is one of forgiveness and commitment.