Ummm.. Writing a poem is a big no-no. It's stalkerish. It's okay to write a poem if you've been in a relationship for a while, but not okay to write a poem if you're not in a relationship with a person. It's safe to say that your friend freaked him out.
...And the fact that he is in a relationship with another girl just makes it even more stalkerish. Tell your friend she made a boo boo.
Sources: Personal Experience
I will do my best to reply with an educated, humble and honest answer. Ultimately, it is up to you whether you want to listen to my advice or ignore it completely. Sometimes, my advice may be wrong; occasionally, it will be right. Regardless, I want to do my best to give people answers they are seeking.