The Bible doesn’t say anything about masturbation directly, and masturbation is not necessarily wrong in itself. Although masturbation in itself can be neutral, it can easily lead to activity that is not good. You can read more about this in this article: Is it OK to masturbate?
If you masturbate a lot, or regularly, you will start to think more about sex and be preoccupied with sexual feelings and satisfaction. Even though you don’t use pornography, it could still be more difficult to keep your mind off sexual fantasies. This is why we advise you to try to avoid masturbating too much. You can read more in this article: A story about masturbation and sexual feelings.
Best wishes