Adrian can't blame Cassidy for thinking the way she does.
Five years of neglect and mistreatment would definitely crush her entire being to the point that it could no longer go back to the way it was before. He could only wonder how she managed to cope up with everything. For letting her be, he hates himself. He finds himself more than undeserving - he is unlovable.
Even then, Adrian decided to condemn himself in silence and focus on making things right instead. He already wasted a lot of time, and if he became too absorbed in his self-loathing and hatred, he might end up losing more. That's why he tried and tried to make it alright even when he felt that it could never be right again just like what Cassidy said.
"I-Is it too late now, Cassidy...?" he managed to say despite how weak he was starting to become.
"But even if it is, I'm still going to try. I'll try harder to-"