Answer:
Hi (Name),
I'm so happy to hear you're graduating! I'm so proud of you for making it this far. However, I dont think I can make it to the graduation ceremony. I have (insert event) that i have to attend. I'd really like to go but these are important because (give reason #1.) Also, (reason #2.) I'd love to go but it's just (reason #3.) Thank you for being so understanding! I really wish I could go. You're going to look so amazing, send me lots of pictures!
Sincerely,
(your name)
