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. Your capacity to set appropriate limits when needed in your child's future development will be best assured if you resolve misplaced guilt now. Unresolved guilt is often the culprit for disabling parents of their authority, resulting in misconduct and other difficulties of childhood. Seek help to recover from the abuse in your marriage. Withdraw your energies from your ex-spouse.