You masturbated and watched porn too much and now it's too late. Seriously all that shit, makes you feel less natural about the real thing. I bet you are a fucking ace imagening sex while spanking your monkey but when it comes down to show it's so entirely different from what you've made yourself used to, it makes you too awkward to function properly.

Most likely it will eventually wear of enough for you to get it up and perform to minimum expectations, i.e. at least making you and your girlfriend orgasm. But it will never be as good as it could have been. Once shit gets inside your head, it never fully dissappears.

.....Enjoy your sexlife. ^^