Unfortunately, once you are Divorced, and things are said and done, you have absolutely no say so as to how your EX spends his money.
Yes he is being frivolous with his money, but in all honesty it is his money.
I also think that once a child becomes 18, child support stops also.
As your Son is 18, perhaps he can ask his Dad for some Summer clothes and financial help.
When my Husband was gone, my two older kids got Summer jobs to pay for their extra stuff, and they both had part time jobs after school.
Now that he is home, we help out when we can, but they are adults now and have to be responsible for themselves. They are both in College and both work also.
Renee, as a side note, kids appreciate things more when they have to work for what they want.
There can be no testimony without a test. I am praying to go through this test and come out the other end with a new and better marriage then before.