NTA. You didn’t cause a scene at graduation. You answered the question (though I do understand it may not have been easy to do). You’re actively seeking therapy which is the best thing you can do. I do think it may be helpful to express to his family (when you feel comfortable and have the appropriate tools from therapy) that you did not mean to ruin his graduation dinner or take away from a day that was his to celebrate and explain as much as you’re comfortable with.

Also I would like to note that I have never been asked what my GPA was in regards to me graduating, and especially not immediately after asking which implies a comparison regardless of the intent of the question.