if you're unsatisfied with your sexual relationship, that does sound like a problem. Yes, there are indeed men who prefer books/films to real people, and no, they don't invariably get bored with it. This may require some therapy, or at least a good deal of self-analysis on his part, which will work only if he himself feels the need to change. Evidently you being upset isn't a good enough reason for him to do so.
It's worth repeating that masturbation is normal, more so for men, and it will often involve porn of some sort. But preferring it to contact with a human suggests something is wrong. I don't think your worry is unreasonable.