Hello and Thank You for using Just Answer. Unfortunately, your son has already been exposed to a plethora of sexual images. The more he views such images and draws explicit pictures, the more curious he will be and may have a desire to experience some of the actions he has observed himself. Nowadays, parents need to have the "sex talk" with their children around the ages of 10 or 11 so that the children will hear correct information from their parents instead of from friends or from personal exploration. Your son is probably very embarassed to talk to you about sex as he is entering puberty and developing feelings for the opposite sex. If you and your husband are finding it rather difficult to talk to your son about his inappropriate computer habits and drawings, then seek professional assistance from a counselor or a psychologist that can assist your son and his desires. There may be deeper rooted problems than on the surface. In today's teen age world, young girls practically throw themselves at our young men through the clothes that they wear, things that they say, and in images that they text. Maybe your son is confused about his own developing sexuality. Ask your son's pediatrician for a referral. You do not have to pull your hair out over this situation when there are trained professionals who can provide intervention and coping strategies for you and your son.
Hope this provides you with some insight. Have a great day!!!