That seems to me to be where these conversations always break down: “what if she assents, but in Czech?” Um, then you stop.
Look, if you don’t fuck her, and all the other dudes she pulls this shit on don’t fuck her, eventually she’s going to say “gee, why am I not getting any?” and someone will tell her “probably because you keep saying ‘no’”. And chances are it will take longer for that to happen than it will take for you to find someone who’ll say “yes” straight out.
And I’m a straight dude, Fotheringay-Phipps, I do know what it’s like for men.
You keep adding “oral” and ignoring the “or by clear, unambiguous action” part. I never have sex with my girlfriend if I don’t think she’s down with it. If I’m not sure, I ask. That said, looking back, I’m pretty sure I have had affirmative oral consent almost every time; most of the rest, consent was obtained by SMS. But it wasn’t like the robot lawyer approach I’m pretty sure you’re envisioning.
And all that “the existence of a dating relationship between the persons involved or the fact of a past sexual relationship should never provide the basis for an assumption of consent” means is that you can’t claim that the fact or duration of the relationship constitutes consent. It doesn’t mean you can’t bring to bear everything you’ve learned over the course of the relationship about reading their signals.
If you’ve discussed it, that’s more than just “the existence of a dating relationship between the persons involved or the fact of a past sexual relationship.” The affirmative consent is in the discussion.
Which it actually is. Of course, with a long-term girlfriend you’re likely to have a pretty good handle on what is and is not consent.
Unless you are determined to declare any reasonable interaction normal humans are likely to do in advance of sex to be ambiguous.