Y/N was out on a hunt with the Winchesters, searching for a vampire coven that had been terrorizing a small town not far from the bunker. Castiel came to the bunker in search of Y/N but realized she wasn't there. That gave him the opportunity to look at something he had been meaning to see, he went into Y/N's room. He remembered seeing her writing in a book and it left him curious as to what she was writing about. It didn't take him long to find it, he picked up a small black journal that was on her desk. He sat down on her bed and opened it. the book contained pages and pages of short stories, journal entries, and poetry. Castiel was amazed at how well she could write. He had known Y/N for some time but was unaware of how talented of a writer she is. He read almost all of it, what intrigued him the most was a poem she had written for him called fallen angel. 

From the heavens he fell

Wings torn and burned

hands reaching out 

pulling him toward the earth

falling in flames, like a meteor

a fallen angel, no longer immortal

a man who chose to be mortal 

a creation of the lord

words spoken long ago

a fallen angel 

staring at gods creation, with no words to speak

only tears fell from its golden eyes

speechless and astonished

Castiel thought the poem was well written, and after reading it he couldn't help but feel something towards Y/N. 

"Cas? what are you doing in my room? and why do you have my journal?" she said, crossing her arms. Castiel put the journal down on the bed, got up, and without hesistation he kissed her. Y/N was surprised at first but then melted into the kiss. they pulled away after a minute. "I love you too Y/N" he said. Y/N smiled and kissed him again. Dean and Sam saw them and smiled to themselves. They were happy that Y/N and Castiel were together now.