It depends on how you interpret it. While reading it, I interpret it as he means to say that love is as innocent as a person can make it. When he states she walks in beauty, he is most likely referring to the idea that she is beautiful and has a innocent lifestyle. My apologies if this is not the answer you are looking for.
There are no "shown" because you didn't give us anything, nobody can help without resources for questions like this!
Answer:
I don't know for sure so I am sorry if its wrong.
Explanation:
The preposition is "on". The prepositional phrase is "had spent many hours working on". And it modifies the word "their"
Again I think I am wrong so I am so sorry.