Hey
Assign this voice a persona separate to you (I call mine a gremlin) .. that way when it says stuff like "no -one will know" you can say "I'll know". You can treat it as a nasty person you don't want to spend time with.
It's also best not to engage with the voice as it is a losing battle. Get into the habit of telling it to "sod off" firmly and with practice it will get quieter.
By the way the "no-one will know" thing is a typical addictive behaviour; might be worth doing some reading on addictive behaviours to give yourself some insight to help you.