Take your time. There is no need to visit your son at his grave. You can just sit & take a moment to visit with him anywhere you are comfortable doing so. You can put flowers at home that are for him and he will know your thinking about him. His Spirit is always with you. I believe that your body is just a shell. Yes I understand that it makes its different when you have sopmthing to go visit, like his resting place. But his Spirit will always be where you are. Maybe you would like to make a special spot at home where you can sit & visit with him? Or is there a local park where you would of liked to take him? Maybe you could sit there.
Just know that he is with you no matter where you stop to visit him. I think he will understand if you find it difficult to visit his resting place at the moment. He would want your visits to be happy, not hard.

HTH's

xoxox