Do not second guess yourself regarding your decision to divorce. Clinical studies have shown that single parent families are quite capable of producing loving and well-adjusted children. You are not deficient. You are enough for your son's healthy development. Do not create unrealistic fantasies for your son, and he will not be obligated to fulfill them.
Children can cope with the reality of life when they are lovingly supported in doing so.
Sensitivity is spawned from life's troubles. Do not avoid discussing questions and feelings he will have about his biological father, but do not confuse him with expectations that his father fulfill his needs for parenting in any way. This would be a setup for unnecessary disappointment. Research shows that when a single parent is capable of loving authority, children flourish. Become the best parent you can be.