I went through a similar situation 2 boys now 17 and 15 with a similar dad. We had a family meeting at the table. It is important to listen to what you son wants and his expectations for spending time with his dad. Can a compromise be met (as far as activites)? The respect issue needs to deal with consequences as he is old enough to understand that you are both willing to speak to him as a young adult and if he wants this treatment, he needs to be respectful. I would not try to convince or change you ex, it comes across better hearing it from your son. Ultimately, the both will come to a decision and then you may be faced supporting your son over your ex. He has a legal right, but if forced, you son may rebel, runaway etc.
I feel so much for you as this is so hard.
Best of luck