Greg, I know this trauma from when I lost my mother. Oh, how I envy that your dear love had a chance to say good bye to you in a way that suited her dignity. To lose a loved one is not a good thing, but it sounds like it was not unexpected. The grieving that you did before that final moment is valuable, but I can't honestly tell you that mourning ahead of time helps. Mom's decline give me years to prepare, but that ton of bricks is waiting to fall just the same.
In the days ahead you will have your share of grief, and it is natural for us to mourn a loss. Right now, you are powering through for the rest of your family. But you will need time for yourself, too. The next several days, weeks, months,... will have their brutal moments. But as time passes and the immediacy of your loss fades, you will be able to look back at the good times and remember your good fortune for having found a good long-term partner. It will represent a level of healing when you will be able to look to the future again as you enjoy gatherings with your family. You will never forget - but you might just find peace in the memories you made with your partner and the memories you can still make with your family.
It is now almost 40 years since I lost my mother and I still think of her from time to time. But at least I can look back on the totality of our time together and remember our celebrations as well as our sadness. I can hope for you to find this level of peace with the past. Don't try to force it. Don't try to stave it off. Healing comes at its own pace for each of us. But Greg, know that peace CAN come if you let it.