I am assuming you divorced in MA.
So did I.
If your divorce decree says child support ends when they attend college, I'd say that's your Bible.
I am actually paying both child support as well as college expenses (not to mention covering the medical insurance, and life insurance on myself).
So it sounds like you did ok here actually if you want an opinion.
I was fortunate that my daughters each have gotten scholarships and my ex wife would have to pay 1/2 of whatever the price was, and she can't afford to pay for anything. So so far, it's not been bad.
Personally, I think it's crazy that legally they can put you on the hook for college, when if you were still married, it would be what you can afford. However, my opinion changes nothing.
If I were you, I'd be talking to my lawyer to be sure it's crystal clear what you are responsible for and what you are not.
It sounds pretty unlikely you'd be on the hook for Harvard if your financials clearly show that was impossible for you to do.
As far as I have been told, MA is unique on this child support after 18, and basically paying for their college education. My gosh, I'll be paying "child support" til my daughters are in their mid 20's.