Apologize, so he knows. And so you can lift the weight from yourself. It's all you can do at this point.
I did the same with my mum. I wrote her a letter because it was too hard to say in person, or on the phone (I don't live anywhere near her anymore).
I still feel bad sometimes, because I don't think she gets how sorry I am, or I can't express it with words.
But you never know what can happen. Good luck. :)