Its not instant, its not overnight. There will be hours when you dont notice the pain, there will be days when you cant do anything but hurt. But time will make it bearable. this could be weeks, months, maybe even longer. But time passing every day will be the only medicine.
hang in there. last year handed me a a lot of loss....it took me a year for the pain to go away. now, like i mentioned before i'm dealing with my grandma in a similar situation as you did with your grandpa before he paased. i've been trying to block out the pain, but it doesnt work.
but what you are going through is normal....it takes time.
Eventually life tends to move you forward, and eventually you'll forget the pain. But he is a part of you, and you will eventually remember, and each time it will become easier.