Porn was always a "wonderful tool" for me. Since I was way too young, I've had sexual urges. And the body kind of wants them satisfied. So even though it's not pleasing, I "have" to masturbate. Porn is useful. It allows me to go into fantasy of not having this body for a while and become a character or change my body in my mind, which makes the mental pain lighten. If I combine that with staying dressed for the whole thing, looking at myself as little as possible, and keeping the sperm inside, it allows me to get my genitals to leave me the heck alone for a while without too much pain. On a toilet or a bed, it feels very bad.
In short, porn allows me some non-aroused periods or rest.
As for earliest reactions to porn, hmm, I don't remember. Sorry.