In Orthodox teaching we learn that all of Creation is good. After each step of Creation, God said that everything is "very good." (Gen 1:31) So what is the source of evil?
Here is how Elder Paisios explained it to a pilgrim.
Evil exists when we make wrong use of the things of God granted to us for our benefit.
It is not bad for someone to have money, but it is bad to be avaricious. Drugs are not an evil thing, when used to relieve the pain of people who suffer. They are bad when used for a different purpose. A knife is a useful utensil, when we use it to cut bread. However, when it is used to hit someone, it becomes a deadly weapon. In this case, it is not the knife which is evil, but the inner disposition of the murderer.
Therefore, we must use everything in the right way, the natural way, not abuse them and go against nature.
Since we are weak by nature, when we are inclined to give in to a passion, we should try to avoid anything that makes us feel vulnerable. We should also be aware that the reason we avoid the causes of our passions is not because they are evil themselves; but rather, because our ill inner disposition does not permit us to use them correctly.
Since we cannot benefit from them, it is better to avoid them, so they do not harm us. At the same time, we should glorify God for His gifts, and blame ourselves for abusing them and thus provoking the evil.