Masterbation frequency of natural rhythm is not harmful. For masterbation , you can use porn/ photos/ imaginations etc. But inspite of natural desires , if you repeatedly see porn as pleasure and with that urges, doing masterbation is bad. You can reduce excessive porn watching , it will automatically reduce your masturbation frequency. You can do masturbation as per your natural rhythm of sexual desires.
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Consult me personally for more guidance . take care !