Regular masturbation causes infertility or not?

No: Although it may decrease the total number of sperm available at the time of intercourse.

Absolutely not: Whoever told you this was either seriously misinformed, or was trying to deceive, frighten and manipulate you. You're almost a grown man, and this time of life is difficult enough. It lets you learn about your mind and body in preparation for being a husband and father, keeps you comfortable and able to focus. Only if you have an obsession with erotica getting in the way of life is it a problem.