Hi Fran
Welcome to the forum

First things first You divorce will have nothing wantsover to do with your sons activies in regards to you clothes.

Is your son crossdressing ?? maybe.
Is it only an experiment ?? maybe

He will have curious mind at this point in his life
It may have something to do with the materials e.g. Silk or Satin
You have to give it some time get as close as you can to your son and try to ensure he can tell you anything.
He will be feeling guilty about using your clothes.
The opton maybe to leave a note with your clothes saying please use if you wish but leave them out for cleaning.
This will let him know you are not worried and you will find out what he has been using

Only you can decide if this is a good idea.

Best of luck in whatever you decide.