@AshuraX well, when you pay more attention to something else than to your girlfriend, it doesn't matter what it is. I mean, I got myself once really jealous of a game, because my girlfriend paid more attention to it, than to me. I never thought before, that that would happen to me, because I play videogames myself, but we're in a long-distance-relationship and we don't have much time for eachother because of school and working and my girl prefered to play hyrule warriors instead of talking or chatting with me. So I got jealous and we talked about it and now its fine.
But as you can see, it is possible to become jealous of a book/game