what is different about his solitude at the beginning of chapter 18 from his solitude while first creating the monster?

I think Victor was a Mr. busy scientist when he is making the monster. He is engrossed in his work. It is a solitude that he craves. His later solitude is filled with guilt, remorse, rage and suicidal thoughts. He is trying to come to grips with his "horrid" creation and what it has done.