Are there any difference in the meaning of between "in secret" and "secretly" in English? What's the difference? They are just different way to express the same meaning.

스럽다 can be added to nouns to make that a noun an adjective. You can also add ~게 to the ~스럽 to make 스럽게 which turns the adjective into an adverb. That's all that I know about -스럽다, but don't understand different between: 비밀히 - 비밀스럽게; 조심히 - 조심스럽게...