Hi there, I am nearly 58 (I still feel 18 in my head) and I have experienced the long-term effects of PIED. If I can offer any advice it's simply this - you simply have to stop...! The long-term effect on your emotional and physical state by not being able to perform as a true male are, at this point in your life, beyond your comprehension, and I mean that kindly.
Your brain is very "plastic" at your age and your porn habit is driving deep memory grooves into your brain that will take time to repair. I have lived for over 10 years with the inability to perform with my partner, the inability to maintain an erection when I have paid for sex (which is another potential route you could find yourself going down - according to recent surveys, 90% of porn addicts will seek sexual services from a prostitute) and it is the worst place to be, believe me.
You are young, you have your whole life ahead of you - you just have to get on the reboot programme or you are committing yourself to a very frustrating and unfulfilled life. It is tough, I am still trying to kick the habit but I urge you to completely reboot. If you haven't already discussed it with your girlfriend then you must, and engage her support. Believe me, just that simple act will kick-start improvement. Then listen to as many YouTube videos on porn addiction and put a plan together to distract your mind and keep your hands away from your dick.
I really don't want you to experience the 10 years I have had ( and still living through) - I am totally on a reboot and will succeed. You can too... GOOD LUCK...!!!!