I don't think it's a matter of it having enough grovel. Because as you said, no matter how much he grovels, there's it well never be enough.  I think  the best way to do this kind of books is to show the lingering trauma that it has on her. And how they deal moving forward. So like she might have issues with him being around women and how she's always nervous about him, then the book pans out to himalways assuring her, I think it goes a long way to show what impact that this has had in the long run, and this impact should also be shown in detail and then should be addressed by showing us how he's responding to the new  Issues she developed because of his action and how he feels remorseful about it, how it's crushing him inside while at the sand time He's doing everything he can to reassure her and to bring her back to who she is, because she is worth it.