I do not feel that your son died in pain. If indeed he died from a diabetic coma, that is a very "easy death." It is very much like going to sleep. You should know that I have given this some deep thought at a Soul-level, for it is an "emergency exit" plan for this current body, which is diabetic.
Some would argue that there are no "pleasant" ways to leave the earth. But the fact is, we all must leave at some time. So, the Soul, often before birth, builds into the dna a method for exiting the body when the time is right. Your son's Soul "built into" his body the genetic pattern that allowed a peaceful death. For there are many nightmarish ways to die, and only a few serene ones.
As a spiritual person, I deeply empathize with your pain and suffering; yet I must also remind you, and myself, that death is a major transformation, a new beginning, and the chance for a new life. Death is not the "end" of everything, as some materialists and mechanists claim. (And they have no "proof" of this.)
The ancient mystical classic Bhagavad-Gita says that death is like changing clothes.
We have come to see it as an unmitigated terror and horror precisely because we have fallen very deeply into amnesia. In the Soul's amnesia, which is part of the will of Love, we forget that we are immaterial, nonphysical Souls, and come to regard ourselves as only mechanisms or developed animals. We are much, much more than both. And very much in modern thanatological (death-) studies implies that the mind does indeed, as mystics have always said, survive the body. We literally have tens
of thousands who have returned from death to tell us that Mind continues after death.
Death is not only a "survivable" experience, but an entry into ecstasy and immeasurable joy. And Love is greater than death; the Love-bonds continue between mother and son, as between other relatives and friends. You will see your son again, happy and alive. Meantime, he wants you to live out your fullest and most productive life; he also wants you to find the most joy that you can create in your life on earth.
Earth is a very difficult and challenging school. God says that it is okay, just fine, if we stop believing in Her, or even, for a time, lose all motive to live and to serve. She does not condemn us, and the spark of Love that She creates in our hearts never goes out. It simply waits, with unimaginable patience, to be fanned into a warm flame of expressed Love.
In the shorterm, it might be therapeutic to form special bonds with other people, or other creatures; this is what your son wants for you.
Lovenergy changes forms many times during a life, but It never dies. So, you can take the Love of your beautiful heart, and enrich many lives with it; our poor little planet is starving for Love.