Other addictions

Its just your association between the two actions, if you do this then do that so to say. Our minds are very good at conditioning associations, just like Pavlov's dogs. Maybe you first started doing this to take your mind off the post nut clarity, but soon it became a problem on its own?

 

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Similar experience.
In my case, every time I smoked I had to PMO.
Every time I ate junk-food, I also had to PMO.
Every time I X,Y,Z, I also had to PMO.

These are just triggers.
One bad habbit build on another bad habbit.

Break the chain.

Re-wire your brain by changing your habbits.
Start exercising, cold shower (if you want to), read books, most importantly and the biggest winner here, is to do a dopamine detox. You can watch Youtube for this one as a mini-guide.

Basically try to stay in the middle of the room for 16 hours (from the moment you wake up until you go to sleep) - going to the bathroom & eating & drinking water.
But besides that, don't do anything.

Just sit in a room.

No phone, no PC/laptop, no GF, no talking with people. NOTHING.

This will get you BORED a lot, but it will also RESET your dopamine receptors.

When that happens, reading a book seems FUN.
Exercising seems FUN.
Cold showers are AWESOME.

And guess what. When something it's fun, you are more likely to do it!
I hate the word "grind" because it's so BS. Just change your perception about the activity you want to do and make it FUN.

FUN FUN FUN FUN FUN wins. All the time.