Since he is over 18 he is an adult . You dont have a say in what his father does as your divorced .. Yes its sad that your ex is leaving everything to his new wife but he can do what ever he wants to.

Why did your ex tell you what his plans were with his monies and thing after he dies? Did you ask or did he offer the information?

I dont think you need to get involved honestly. Thats something your ex need to handle.

Maybe you should sit down with your son and show/ tell him once you die X monies and or life insurance etc will be given to him ... Maybe it will spark your son to ask his father what his plans are.

Good luck