I'm falling for my friends boyfriend?! ?

So my friend is dating this guy. They have been together for 3 years. Anyways we became really good friends. But now I'm starting to like him. Other than his gf I'm the girl he talks to the most often. He has implied that we thinks I'm.pretty. He also called my beautiful & he whistled at me. It was all in a joking friendly way but I think I'm interpreting it differently. Also, I had to dress up like a young school girl for a project. He told me I reminded him of the school girl porn stars with high pigtails. I'm soo confused should I just stop being his friend?! I don't want to get involved at all so I think I should stay away