If you determine that you are confident that your son has not been molested in the past, then move on to treating this as you would early sex between heterosexual children.
It was really bad, and I have deeply regretted not telling anyone in my family about it when it was happening.
You have to think about telling what happened to you to the rest of your family and the consequence of that; or not telling and the consequences to you.
Finally he told me that he would be continuing to do this if possible.