Love and loss have a profound effect on our senses, memory, and well-being. I think all of the things you’ve pointed to as possibilities for not being able to remember are relevant. They are all real candidates for why he may be difficult to remember. Yet, our memories are not like set stone. They change and shift as we recall and add information to our recollections.
My advice is to pull together a living biography of your grandfather. Talk to those who knew him, ask for stories — particularly stories where you might have been involved. Search for photos, stories, and artifacts of his. Everything has the potential of being valuable. Talk to your parents about their stories of him, and any family members alive that knew him.
Just as with biographies we read we come to know someone through the particulars of their life as seen through other’s eyes. The search for photos, videos and the like are important as hearing his voice and seeing interaction can have a great impact on constructing a person’s story.
If you feel inspired there are ancestry tracing services, such as these, that can take a bit of your DNA and help you learn about your family tree — and, of course, your grandfather. All of these methods are ways for you to construct an understanding, honoring, and recollection of who your grandfather was.
Wishing you patience and peace,
Proof Positive Blog @ PsychCentral