Hum? Sounds like my ex! He too as a 25 year old was sleeping around with 17 year olds. I think they are easy targets/victims. Try to remove yourself emotionally from what he is doing with his life. If he is like my ex he will only continue to reap more destruction. Don't bad mouth your ex to your son, that could easy turn on you. Allow visitation but no sleep overs. If your son and ex could have one-on-one time together that would be ideal, better for everyone involved.