I think I'd personally be very cautious with someone who wants to "help out." In my opinion this seems a bit like seduction. Maybe it was innocent seduction between your friend and you. Maybe it wasn't. Only you and your friend know the answer to that. I don't know if your friend is straight, bi, or whatever. But you should never allow yourself to do something you don't want to do; even if it "might" be fun. You should repsect yourself to say "no" when you mean it, and "yes" when you do want to be with someone. I do a bit of seduction myself, but its always been with the partner I had at the time; not with a friend, but that's just me.
From your reaction I guess you find it awkward when he unzips your pants. Just say no, but I understand that you like common wacking, so I'd say you should do that part.
I find it interesting that the fuel for the mutual fires here is lesbian porn, yet your friend, a guy, is obviously very curious about you, another guy. Nothing wrong with that, just an observation. And no, I don't view this as gay, but then again I'm not big on labels. I say sexual exploration is sexual exploration. Sex is meant to be enjoyed, and if you're enjoying what you're doing, why analyze it? You're a consenting adult. So...
I'd love to be 15 again and wank with my mates, now its hard enough to get a fuck buddy to wank with.