Did the Friday girlfriend abused you? hehe
No, seriously, every men will go through with some of those issues some time in their life. Sometimes its performance anxiety, other time you might just tired, or just no chemistry with the partner. Although your brain be telling you to do her in 7 different ways there are lot subconscious stuff we are clueless.
More problematic ED happens when you cant get it up even on your own, watching porn, or whatever turns you on.
EDIT: of course this does not mean you should not take AI and hcg during cycle, as advised and explained here:
My First Cycle: Planning and Executing a Successful First Cycle