Any chemists who can explain this?

I am not a chemist but I have some general knowledge about addictions, maybe you will find it useful. So it will be oversimplified but it could give you an idea why this happened.
In our brain there is a thing called "reward system" it exists to make you motivated to eat, sleep, have sex etc. Simply when you do something which is good for you your brain releases "happy hormones" (for ex. dopamine) which makes you feel good. When you are watching P you are flooding your brain with these hormones (especially when edging), so your brain determines that something is wrong and reduces the amount of hormones it is secreting. That is why when you are exposed to P you will feel tired, lazy and not motivated to do anything else. It also reduces amount of these hormones which you get when you do other pleasurable things so you cannot get that "euphoric high". After you NoFap for couple days your hormonal glands are back to the previous state so they can produce enough hormones to cause the "euphoric high".

 

We have the runner's high and all the other natural highs which happen if we are healthy, not on any drugs and ingesting healthy drinks and foods at the right levels. I have noticed optimal mental health when exercising in the national forest with healthy organic teas, green foods and other optimal inputs.

The erotic material tends to overload the memory and limbic system, the "ape" mind and as usual the neo cortex takes a back seat to the primal desires and impulses. There is nothing more pretty to me than a healthy athletic young woman, without clothes too much of a draw for my senses. In the real world the natural limitations of girls and women not that healthy and not available for our ogling would put a halt to that.

 

Dopamine when surged again and again by watching P, causes to weaken the dopamine receptors. Now, even if dopamine is surged, you don't feel rewarded, wanting for more surge...

 

Effects of external and internal stimuli all depend on the person. Ordinarily healthy young men should feel better with healthy inputs, a good diet plus exercise.

External effects like speaking or taking a walk with a beautiful healthy young girl and you get another positive vibe, of connection and friendship. Some women are just so inspiring.

 

Maybe @Angus McGyver can enlighten us. Sir, please?

 

@Suki pretty much explains it all quite well (so no further explanation is really needed for that) but I would still like to throw out a warning for those leafy greens that are supposed to be so healthy for you but I have recently found out some interesting info that really shakes those health-claims at its foundations.
Leafy greens contain a lot of oxalates or oxalic acid forming compounds with the body's minerals (making it an oxalate-ion of some kind, i.e. calcium-oxalate, magnesium-oxalate, etc). Unfortunately, it can form compounds with the body's minerals in may of its organs, primarily the small intestine and kidneys. When it binds with the calcium in the kidneys, it forms large crystals and if there are more crystals formed than the fluid in your urine can dilute over time, kidney stones will form, causing you large amounts of pain.

So, leafy greens are in fact more of anti-nutrients than nutrients and should be kept to a minimum. Even most fruits (but coconuts maybe) should be eaten very moderately because of the concentrated sugars, insulin-spiking properties and in some cases lectins.