I've gotta ask a really silly question, what should he do to fix what he's done - because I honestly can't think of a thing!

Only YOU can answer that. Perhaps ask him what he thinks he can do to help repair the broken trust too.

This really is about what YOU can live with, what you want to happen from here and how you want it to happen.
The only person who needs to be satisfied with his answers and explanations is YOU. We can't tell you what to believe or how to feel.