Hello. I believe I can be of help to you with this issue.
His wife will have to take the lead in helping him get treatment---under the threat that if he does not, it may result in a divorce. She can do this under the premise that when she agreed to marry him, the vows were based on an understanding that the both believed deeply in having an exclusive, and totally monogamous relationship. He is sexual addiction behavior is grossly violating the terms of their marital vows. In other words, when she married him, she did
NOT "sign on" to accept a man with sexual addiction problems. He has always had this problem (since his late teens) and kept it from him. He can externalize blame for the problem all he wants (e.g., marital stress
, lack of communication with his wife) but if he does, this attempt to escape/avoid responsibility is simply to be seen as part of his behavioral disorder.
His wife should insist that they enter marital therapy and that HE enter individual psychotherapy with clinical or counseling psychologist or clinical social worker who specializes in so-called addictive behavior. There are self-help supplements to therapy (not replacements) that can be helpful---both your son and his wife should review; as a parent, you may find the information valuable and supportive as well:
My main point is that unless your son is motivated to get help, it is up to his wife to place maximum pressure on him to do so, or face the possibility of separation or divorce if he does not. You need to assess whether you are on the 'same page' with his wife about what needs to be done. That is, the more your son's social support network is unified and 'gangs up' on the problem jointly or collectively, the more likely he is to get help.
What is your son's frame of mind regarding his problem? Other thoughts, reactions to what I've written so far?