Lately, I have felt depressed, ashamed, and guilty before God; because of my sins, particularly contemplating adultery in my thoughts. I am a Coptic Orthodox, fairly knowledgeable in my Church's beliefs. Is it alright to seek help from a Christian psychologist outside my Church whom I have already contacted and who has offered his support and assistance? I have already purchased the book he has written. Being fairly knowledgeable of the Coptic Church teachings, I think I am fairly capable of refuting unorthodox beliefs, and if not, I can always ask.
The first step in repentance is identifying the sin making a resolution to resist it until you succeed to rid yourself of it. This needs a lot of prayers to God asking Him to give you the strength to overcome this sin without weakening or procrastinating on the way.
In your pursuit to overcome your sin; you have sought to read some materials that though might seem helpful but could in reality be very dangerous. The person you have mentioned is a Mormon. All main stream Christians (Orthodox, Catholics & Protestants) consider Mormons as members of a cult that we do not call Christians at all. Mormons believe in polytheism, three gods, as different personages; that our Lord Jesus Christ, like Lucifer and all demons is a spirit born in the spirit world as babies to our man-god 'Heavenly Father and his goddess wives. You can read more about Mormonism in "World Religions and Cults" at http://www.suscopts.org/servantsprep/servantscorner/materials.html.
Beware of seeking spiritual help from someone who quotes the book of Mormon '(see 2 Nephi 4:18; Mosiah 4:29-30 etc.)', and Joseph Smith in his spiritual and psychiatric teachings. Do not fall in this trap; for the Holy Bible says "Beware of false prophets, who come to you in sheep's clothing, but inwardly they are ravenous wolves" (Mt 7:15). Your statement, "Being fairly knowledgeable of the Coptic Church teachings, I think I am fairly capable of refuting unorthodox beliefs, and if not, I can always ask"; it is not a matter of your capability to refute but a matter of deceit. I urge you not to seek any further spiritual help from this person.
The article he wrote and the points are not new; but are common points known to psychiatrists and all those who treat addictions.
I recommend you read 'Steps of Transformation: An Orthodox Priest Explores the Twelve Steps' by Fr. Meletios Webber. Although the book deals mainly with the struggle to overcome alcoholism; yet it is useful to overcome any addiction and to grow spiritually http://conciliarpress.bizhosting.com/steps_of_transformation.html.
His Holiness Pope Shenouda's book 'The Life of Repentance and Purity' is also an excellent source of material that would help you in your struggle. You can read it at http://tasbeha.org/content/hh_books/Repentan/index.html.