Most Helpful Guy
You don't sound like you're happy in this relationship. Remember that just because you "like" someone, it doesn't mean that they're good for you and it's a good thing to know when to stop yourself. Trying telling him you don't want to do those things anymore and if he doesn't respect that, he doesn't respect you. But you won't know till you tell him.
Most Helpful Girl
If you don't feel comfortable doing it, you really shouldn't be. If a guy is going to stop liking you over that, then you really should move on anyway. that's just my opinion, if a guy can't like you without nudes, then that should tell you something anyway.