I read a site recently about this and it seems pretty scientifically sound.
http://yourbrainonporn.com
One of the things it says (maybe its the only thing it says, I havnt read any more of the site) is that porn lowers dopamine levels in the longs run.
Dopamine is the brain chemical that is to do with reward. When you see a hot girl, have a cigarette, eat..anything pleasurable basically, dopamine levels rise during this time. This is what makes you want to do this the next time.
However, like any drug that is continuously used, the brain becomes tolerant to OVERstimulation. Porn raises dopamine levels a lot because it is SO sexually stimulating. Plus you can watch as much as you like, see as many different girls as you like, all with no delay at all (as soon as you feel like it).
This causes high dopamine because the brain is thinking "this is fucking sick!. I am having sex with all these girls!"...but your not really.
Over time, you get tolerant to it, so you get less of a dopamine spike everytime you watch porn...so less pleasure. but this does not mean that you no longer want to watch it because the reward pathways are already set up.
You basically get pleasure from anticipating watching porn, but no longer get as much pleasure as you used to from actually watching it. This is why the first time you watched porn was AMAZING!! and now its normal. And it's why you want to look for different, more extreme porn...because this gives you that dopamine spike that you used to get from regular porn but no longer do.
Anyway, I think that if porn is now normal when it used to be "AMAZING!!" then seeing a hot chick walking down the street can't reeally excite you hardly at all. I mean you've been watching naked chick fucking guys most nights of your adults life...this is just a girl wearing clothes! boring!
I think cutting the porn will make me aroused more easily during the day like when I was 15 and will make me want to approach more.