It took me about 5 years to stop cringing whenever my mother was mentioned in a conversation. She passed away when I was 31 and my daughter was 18 months of misdiagnosed colon cancer. This was back in the mid-70s when doctors still believed in the notion of female hysterics (they still do today). She would complain of pain in her stomach, and he would tell her it was just her "nerves" and prescribe Valium. Turned out her "nerves" was colon cancer. Thankfully, she lived another 5 years after her diagnosis. But it could have been longer if it had been caught earlier.
My mom and I were never as close as you were with yours which is probably why the pain of her death mostly subsided 5 years later. She was a perfectionist for whom whatever you did was never good enough. So I've been angry a lot with her over the years for not loving me the way a mom is supposed to. She didn't know how to show affection, so I very rarely got hugged. But I have learned to forgive her, given how she was raised. I was more angry with the medical system and her fucking doctor.
In any event, thanks for sharing your story. And my deepest condolences on the loss of your best friend. I have no doubt that she is with you on some level of existence and always will be.