Take your time.
Your life just changed in a very drastic way and all of the feelings you are feeling right now are completely valid- anger, sadness, fear- allow yourself to feel them all.
Surround yourself with support. If not a person close to you, an animal, if not an animal, an item that brings you comfort. Eventually these fresh wounds will scab over and you'll have the capacity to invite more in.
Know one thing... nothing, not one single thing, did you do to deserve this diagnosis. Even though it may feel this way now, know you are no lesser than because of it. It is going to get better, I promise.
Once those scabs heal up and you find yourself feeling a little more balanced, accept this diagnosis as an opportunity to live deeply and fully. Identify the joys in your life and really pay tribute to them, flourish with the joy they bring you. Identify the negative aspects in your life and find the strength to release them back into the universe. You don't need them.
One day you will be able to take these memories, the ones following your diagnosis, and you'll pack them into a shoebox and bury them in the backyard. You'll remember them sometimes in a fleeting manner, but the next time you dig them back up will be to help someone else newly diagnosed... and to let them know everything is going to be okay.
It gets better.