This part doesn’t make much sense to me.
Way back when I was in college-- I never returned home over the summers – so I really didn’t expect to see much of my own kids after they went off to colleges on the opposite coast. My son did come home for the first two summers, but it was unproductive time – he pretty much took up space on the livingroom couch. My daughter was more adventurous - she found great internships & spent two summers abroad.
But nothing I chose to do changed the financial understanding I had with my parents way back when – and nothing my kids chose changed my financial understanding with them. I knew what my budget was and my kids knew what they could expect from me. I wouldn’t have increased my parental school-year contribution to compensate for under-employment during the summer, nor would I have reduced my contribution due to a kid earning more than anticipated.
I think your question is mostly about the emotions you are feeling with your son’s choice — and that’s what most of the other parents on this thread are rightfully responding to – but I think whatever choice your son makes, the financial consequences should be his own responsibility. That’s part of the package of making decisions as an adult.