Why do you have to deal with anything to do with him?

Elle

Decades-long husband skillfully deceived everyone around him regarding his sexuality. It completely bamboozled me because my spidey senses suggested something was awry, but friends and family reassured me that I had an active imagination; I thought I was going crazy.
With the help of a private investigator, I learned the truth. ..he was having anonymous sex with men. This had gone on the entire marriage. 
I left him and divorced.
At the time of divorce, I had three very balanced and successful young adult children
.Not that I care, but ex clearly developed or at least now openly has shown his substance abuse issue. He was so out of it recently at his company holiday party that his coworkers had to carry him to a car and deposit him in a hotel nearby. His coworkers reported this to me because they are concerned I have no contact with him and don’t intend to in the future.
  His appearance has drastically changed. He’s clearly on steroids, extreme workouts, and major weightless. He now has tattoos on about 25% of his body after never having a single tattoo. Question 1: Do these appearance changes mean he is out of the closet? Is it common for men to let​ all of us hang out and become drug users after they come out? 
Also, one of my kids has inexplicably seemed to change personality. There is no question about the child’s sexuality, but the ex is bringing this young adult along on his new,  completely out-of-character trips. Ex has no friends, and this child is his only ally. Example: two recent trips to a country known for narco tourism. Together, they attended an LGBT~ performance by an LGBTQ performer in another narco tourism country famous for cheap cocaine.  Based on frantic dancing videos posted on social media during this trip, I’d say there is a substance abuse problem.
Ex has done a great job of trying to alienate my kids against me. I’m not sure how to approach my young adult about the influence of his gay father and drug use.