This isn't a fanciful hypothetical, it's not a case of someone who has had non-consensual sex reaching using a pre-existing relationship or previous sexual contact as a defense. Guilt is now presumed, so if someone is accused, previous consent is irrelevant. This
should be the case, but only
if it is the case that a lack of consent has to be established first as is the case with a presumption of innocence. The legislation, White House policy, and current university policies are pretty clear - if you decide to accuse your husband of sexual assault for groping you (as is now your right, under law it would not be a false accusation), he would be expelled.
While there are hundreds of cases of men being expelled for similar situations, one in California is particularly indicative of how things are likely to play out:
http://www.thefire.org/sexual-assault-injustice-at-occidental-college-railroads-accused-student/
A first-year student was lucky enough to have unambiguous, rock-solid evidence of consent including text messages to friends that "I’mgoingtohave sex now" and to the accused asking if he had a condom. There was also clear planning via text messages of the meetup and a friendly relationship after the encounter. This was enough for both the DA and university investigator to establish that she consented and understood what she was consenting to.
This was until a professor of the accuser told her that he "fit the profile of other rapists on campus in that he had a high GPA in high school, was his class valedictorian, was on [a sports] team, and was ‘from a good family" and convinced her that she had been raped. The university agreed, and a kangaroo court expelled him on the grounds that she'd had a few drinks, despite the fact that he was just as drunk as she was.
So we have the absurd situation that two consenting adults are raping each other, and if the relationship sours, the first to accuse the other gets them expelled (on the enormous assumption that this will be applied equitably), unless they can prove themselves innocent which they can't do because they can't defend themselves, can't use anything before the act as evidence, and can't use anything during the act as evidence because it's illegal to gather such evidence. It's utterly insane.
Edit: It looks like the university is one mentioned in the legislation as one who has failed to punish students previously, an accusation also made at a federal level. So this looks like what happens when you say to universities "drop the presumption of innocence and find more people guilty of rape or we cut your funding".