Does masturbation cause any diseases ?

Not directly: Most of the old wives tales about masturbation are of course not even close to being true. However, you can cause skin abrasions with too frequent activity and you can have reactions to some lotions or creams used during masturbation.

No: Anyone who tells you otherwise -- even a "spiritual guide" -- is lying to you. I'm sorry there are people like this in the world, and the fact that you have asked suggests to me that you're developing the discernment you'll need to survive in a world full of foolishness and malicious deception. If you're obsessed with erotica so you can't work, we can help. Otherwise, enjoy yourself.