Memorise this Gurbani Pangti and recite it loud when such thoughts occur:

ਨਿਮਖ ਕਾਮ ਸੁਆਦ ਕਾਰਣਿ ਕੋਟਿ ਦਿਨਸ ਦੁਖੁ ਪਾਵਹਿ ॥

For a moment of sexual pleasure, you shall suffer in pain for millions of days.

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ਘਰੀ ਮੁਹਤ ਰੰਗ ਮਾਣਹਿ ਫਿਰਿ ਬਹੁਰਿ ਬਹੁਰਿ ਪਛੁਤਾਵਹਿ ॥੧॥

For an instant, you may savour pleasure, but afterwards, you shall regret it, again and again. ||1||