I think sincerely asking for forgiveness for not attending the wedding is the only way to go.

I can’t think of a reason for not attending my daughters wedding, and I don’t know if she would forgive me. (Maybe if she was marrying KKK member and guests were required to wear KKK hoods as a dress code). Other than that in my understanding we make an appearance and put up with whatever and leave early if it’s too much. So you must have extremely extremely serious reason to not attend.

So if I decided not to go and clearly hurt my daughter, I’d beg for forgiveness. I’d not expect her to just move on. It’s too painful and embarrassing for a child. And he’ll likely never forget it. My dad walked off the middle of my brothers wedding over 30 years ago, didn’t like my sister in law. They didn’t estrange over it but we never forgot it. there was never an apology. Your son will not forget it but you can change the future by making amends.

I doubt your son doesn’t love you. He likely is hurt embarrassed and mad.