Hi {Receiver},
I’m really sorry for missing out on {event}!
I actually wanted to go, but I {reason for not going}. It probably isn’t a very good excuse, considering how important this event was to you. But don’t worry; I don’t plan on missing the next one. Even though I wasn’t there this time, you can always count on me to have your back in the future.
And judging from what people have said, it sounds like I totally missed out. I would really love to go to the next one if you’ll have me.
Sincerely,
{Sender}
{Sender}
