It sounds like you need to build resilience. Think of it like this when a toddler doesn’t get what they want, what do they do? They through a fit. An adult (generally) not so much. That is because of emotional resilience. The adult has learned how to regulate their feelings and take the steps they need to in order to ultimately get what they want. That skill wasn’t learned overnight. In order to build that resilience with reading, you have to enjoy and finish books first. If you like fantasy, read fantasy. Once you’ve developed a habit of reading and built up your mental chops for reading a bit, then you can throw in a book that’s not your jam but will help you grow from time to time. At first, these books will be hard because you don’t like them. So, pick easier or shorter ones. You’ll get so those are tolerable in between the books you like. After a bit more of this, you start branching out more. That may be all you ever do. Or you may discover a new genre that you adore. The key is that it should never be something you force yourself to do all the time. Push yourself out of your comfort zone occasionally, yes, but if it’s a hard slog all the time, it’s not sustainable nor is it good for you.