Hi Absinthe, everything sounds pretty good to me. Your friend is really good, the vocal sounds like it was recorded really well.
I might make the fade-in a little shorter, maybe a couple measures? The backing track has maybe a little too much filter on it, sounds like it's high-passed a little harshly. It's pretty bright in my headphones. I wonder if there's a way to bring forward that cool guitar that does the two notes between vocal phrases? It's really nice, I kept hoping it would come forward a bit more.