It’s completely understandable that you are feeling the way you do about trust. We can accept a lot of things another person may not do but those can be tolerable. Yet when a partner strays that’s creates a grievous disappointment and sense of betrayal.

We always can look back and recognize things we could have done differently. However we all learn as we go and we all tend to choose what we know as we navigate trough our lives. I respect your willingness to see how you may have missed things and would do differently if you could go back. Thing is we do not get a redo and can only proceed forwards with what we learn and hope to navigate better When it comes to trust, that is something that both in a relationship has to work on rebuilding.

In my opinion from reading what you have shared though is the person your husband cheated was in fact himself. Perhaps that’s where the lack of remorse really lies too. Depression tends to come from anger and self disappointment turned inward on self.