We all have stories about those lost..some who were our seniors and lived long lives...some who battled dreaded diseases...it's always harder to cope when it's something that was messed up, but in our grief, we have to remember that doc's are human too and prone to make mistakes. And with all the drugs out there to treat and heal, nobody really knows all that can happen.
My prayers that as the grief process, and it is a process, diminshes that you will be flooded with memories and warm thoughts of all you shared, not what is lost.
Life is a present and it must be shared to be enjoyed. It sounds like you two had grand times together. He lives on in your heart!
Peace and healing to you and his loved ones in this time of loss.