The special relationship in the course of Miracles refers to a romantic involvement, but it can also be any type of relationship where the other person's behavior matters to you more than it should.
Intimate Relationships teach us how to be intimate, but learning how to be intimate in non-intimate relationships is crucial for understanding how to be intimate in Intimate Relationships.
The hole created inside of us due to the separation from God led to a sense of existential despair, which the Mind began to compensate for by the idea of a special relationship.
Commitment is not of the body, it's of the mind, and we tend to make special relationships so important because we've projected our guilt onto another person.
The birth of the idea of the special relationship was a psychological phenomena, as it was a compensation for the existential despair created by the separation from God.
Guilt can be a double-edged sword, making you feel guilty for having inappropriate involvement with someone else, and then projecting all your guilt onto them.
The ego first separated itself from God when we first seemed to have separate thinking from God, and God answered with the Holy Spirit who is within us.