Hang in there it gets easier with time.
My dad passed in January, but he had suffered so for 2 years previous that for us at least, it was a blessing for him to be released from his mortal frame. He couldn't talk, walk, feed himself etc... He had one blind eye but could see well with the other and would often smile when I would go to visit. When he started mistaking my younger brother for HIS younger brother, we knew the end was near.
I have felt his spirit close many times. He is still watching over us.
So is your dad. A holy man once said, "The spirits of the just are exalted to a greater and more glorious work; hence they are blessed in their departure to the world of spirits. Enveloped in flaming fire, they are not far from us, and know and understand our thoughts, feelings, and motions, and are often pained therewith."
And so we need to move on and be happy for the wonderful place where they are.... that way they can truly move on and be at peace.