@allforjoy First, so so sorry for your and your son's loss.
I'm sure you talk about dad often, and clearly in a good light if and when you do.
It's not the same thing, but my cousin died when he was 5. I wasn't born yet, but "always" knew the story of his death.
It was a fact of our family's story.
He was the first person I knew of who died.
Maybe I asked about it.
Maybe our parents told us the story.
I don't remember, but I also didn't understand the gravity of "death."
And even by the time I was old enough to understand, the gravity didn't change my memory of or reaction to my cousin's passing.
I keenly remember feeling that someone important was here. Someone I should have known. I never met him. There are photos from when he was here. Now he's gone and I'll never meet him.
That's how my world was structured, and I accepted it.
It was not confusing or scary or traumatizing. It was a fact just like everyone else in the family.
My advice would be to talk about his father often and in the past tense.
He will know that he never really knew him, but you can insert the illusion of his father's presence in your son's memory, making it real as he grows up, memories of an important person that are almost tangible.
That will be helpful when he encounters doubt, disappointment, resentment, etc. in his later years.
Let his father's presence be a very palpable part of his early memories, the good and caring person that he was, while never shying away from the story of his tragic end and the sadness it brought to you both.
I wouldn't dwell on the facts of his death, but let him know.
Answer all questions he asks, within your comfort.
Understand that, as your son begins to assign meaning to words, it will take some time still to understand the metric to our rhetoric.
Some words, like death, carry tremendous weight, while most others are used casually.
This is news to them. It's not confusing unless we make it confusing.
Like my cousin, your son will learn the gravity of death, gain a greater comprehension of the situation your family went through, but may find that his sensibility doesn't change.
It's a coping mechanism to avoid traumatizing past situations and to build our own metric by which to measure new situations of similar traumas and to assign appropriate emotional, physical, and physiological responses.
Speak of the situation as literally as possible.
To the best of your ability, use your words to share your feelings.
Of course, don't hide your emotions. Rather, when he mimics yours, acknowledge that he's sharing
your emotions and thank him for that support.
Help him label his feelings.
Encourage him to listen to and share his feelings so that his expression genuinely conveys
his emotional state and not the emotions he thinks you expect to see.
(but also, it's okay to mimic, that's how children learn)
Naming the drug and recognizing the goodness of his father will likely help him develop an understanding of drug usage, its dangers, and its users (that they aren't criminals or even bad and scary people, but good and kind people). Most children aren't given the opportunity to understand this, to the detriment of society.
Big huge virtual hugs to you and your son.