Nikki, you have been through a really horrible event (his cancer and its end with his death).
He meant an awful lot to you, so dreams, etc., just make sense. The pain and unimaginable grief are because of how much he meant to you, how real that relationship was for you, how real all the thoughts and feelings tied in with that relationship truly are.
So grieve as you must and know that your grief honors him and the relationship (as long as you don't wallow in it).
You'll be able to climb out of the hole you are in and hear the birds, see the Sun, feel a warm breeze...in time.
Be good to yourself; you've lost the only real parent you ever had in your life in a long, positive way.