Nobody was ever replaced in life, no hole completely filled or loss totally healed. You didn't need a medical degree to know that the human body really wasn't stronger in the broken places. Like any bone, the cracks would always show if you looked hard enough.
Time heals. It's slow and it's painful but it works. Talking helps, going out with other people, seeing friends. She'll be like a book you read long ago. If you trust that if it's meant to be then it'll be again, and if it's not you will wake up one day and realize that you hadn't even thought of her once. And then you'll be free.