Linda- Mr. Flipper here. If you are invited by your ex, first of all, then by all means go for your son, like others say be civil , kind, for your son's sake . There are other events in a young adults life ( early 20's ) like getting married which will necessitate the two of you to be present. View this as a practice dry run, (woops) I think they used that in lamaze classes, Oh! well you know what I mean! Use it as a trial run for other more serious proceedings which will occur later for your son. I went to both my daughters weddings ( witnesses) ecch! in the last 2 years and my wife and I did fine, were just classy and dignified. Something tells me you are the same way. Peace out, and good luck, Mr. Flipper