Lame. At least we know (not you, others) it's not ED now. Even if you feel no nerves/anxiety, it doesn't mean your mind isn't subconsciously. Performance anxiety also occurs subconscious. If you felt horny w/ that one girl and were able to get an erection @ some point in the sex transaction, then you should be able to throughout it.
I remember a thread from a user here in July w/ the exact same situation. I'm not sure what he did to change it, if anything. So you're not alone. It's like a new girl issue sort of thing.
Everything else stands though. Even the ADC thing. I wont recommend pills, but if you want them, they're @ ADC.