First you need to really listen to him and hear him, without interference and judgment. You need to understand much more of his beliefs, his feelings, etc. He needs to feel that you are open to his thoughts and feelings. It is and will be very easy for him to shut down - and pull away from you and your ex. Then you (the two of you probably) need to start out by sharing relevant experiences in your own pasts - being honest - and NOT - saying what your son should and should not do. You need to humanize and personalize the issue(s) that you both see. You need to come across and caring, honest people who love their child. After building some level of trust - at some point - you either may end up with your son opening up about some of the issues and/or you will need to express your concerns - but not in a heavy-handed way. Recognize that he can easily find a strong set of allies through the internet from any device that he has. It is Not Enough to "be right". IF - doing these kinds of things does not seem to be moving you forward, then you should probably both seek out other parents - online - with similar experiences and possibly seek professional assistance. If - interested - read my 1987 writing on organizing men's anti-rape work - at: http://georgesworldonthewater.blogspot.com/2020/05/my-1987-mens-anti-rape-organizing.html - Good Luck! It isn't easy, but it is very, very important!