Michele:
Hello!
I haven't read your other responses so please forgive me if I repeat.
This is about YOUR SON - not YOU OR YOUR EX. YOUR SON wants both of his parents there - REGARDLESS of the problems they are having. He didn't chose one over the other - he was mature enough to recognize both of his parents. Now YOU need to recognize HIS accomplishments and be there for HIM. Imagine how you would feel in five years oh heck - 5 months - knowing you couldn't be mature enough to put aside your animosity for your ex and be there for your son. How would you explain that to people? REALLY?! "I just couldn't face my ex and be there for my son."?
You need to be the grown up here, put aside your hostility towards the man - at one point in your life you loved him and loved him enough to have a son with him - be gracious, be polite, be nice. You do NOT have to talk with or to your ex. You can smile. Remember this is about YOUR SON - NOT YOU.
YOU CAN DO THIS. YOU CAN DO THIS!!! YOU CAN DO THIS!!!
YOU WILL DO THIS! YOU WILL DO THIS!!! You HAVE the grace needed to do this.