One more question: Where does God state exactly that a married man shouldn't be alone with a woman who isn't his wife?
I don't think it states that anywhere in scripture. I was just suggesting that Billy Graham and others have instituted that practice to avoid temptation and the appearance of temptation and improprieties. So, it's not scriptural exactly, but it is inferred from the meaning of scriptures such as 2 Timothy 2:22 (flee youthful lusts) and 1 Corinthians 6:18 (flee fornication).