"No, he is not my friend."
Translation:Όχι, δεν είναι ο φίλος μου.
On this exercise I just left off the article 'ο' before φίλος- I did it on purpose because I thought I remembered reading on another comment thread that doing so was acceptable and that when one says ο φίλος μου it can imply that it is "boyfriend" rather than just "friend." Am I confused?
You are right but the article can also mean that you mean a specific friend you were talking about. For example, you are at the airport with your family and you are waiting for a friend they have never seen. They may ask you when seeing someone: " Is that your friend?" and you can reply "Όχι, δεν είναι ο φίλος μου" meaning the friend we are waiting/i was talking about. Truth is, without context, it is better to translate it without the article (meaning a friend of mine. rather that the "particular" friend), so I added those alternatives. ;)