What part does anxiety play in ED?
Anxiety often plays a part in copulatory ED. How can one know how much is porn-related and how much is anxiety? If you have a strong erection when masturbating without porn or porn fantasy, and with normal speed and pressure, then anxiety is probably the cause. However, it's not uncommon for men to have ED caused by a combination of anxiety and porn-induced desensitization. Not surprisingly, mild cases of porn-induced desensitization can feed into performance anxiety issues.
Some awkwardness with sex is to be expected
For what it's worth, I had a similar teenage experience: early exposure to porn, but found my first real sexual experiences to be awkward and anticlimactic. I experienced "stage fright" and performance anxiety a few times, even when I was with someone I was very attracted to. I think that as a teenager I had enormous expectations for what my first encounters might be like, but did not anticipate that the reality of sex would often generate a great deal of nervousness, awkwardness and confusion, and that managing the mechanics of sex was a more complex task than I had imagined (i.e. I had difficulty staying erect when there were so many things to think about!). Watching choreographed porn or mainstream movie sex scenes had conditioned me to think that it always went perfectly. Perhaps some of it was related to early porn use, but I think many people experience this. The reality of first time sex can be very different to those early fantasies, or to staged movie scenes. I remember a friend telling me that he found his first time difficult because he had always imagined himself having perfect pornstar-style sex, but somehow observing this scene at a distance. He found it strange to experience sex with someone in the "first person", from his perspective. Despite that awkwardness, he got into the swing of things pretty quickly; that girl became his wife, and two decades later they are still together!