Are you sure that he has a sexual addiction? Or is it that his libido is high? Also, is he engaging in reckless sex outside of the relationship? There really is no right or wrong way to handle the situation. Honesty is key. Explain to him how you are feeling and get his take on it and go from there. It sounds like whatever is going on is causing you great discomfort and communication is the only way things will work long distance.