Your question is difficult to answer in a reasonable amount of space. Consequently, I apologize in advance if this is incoherent.
Many people - mainly judges and other people in the legal profession - assert that the (common) law of rape always demanded affirmative, explicit consent and that judges/juries were just worse at sussing that out or framing the issue improperly (i.e. by setting the threshold for consent too high). A good articulation of this view can be found in the Canadian case
R v Ewanchuk (read L'Hereux-Dube's judgement if you're just looking for the cliff notes).
Others have asserted that the above is essentially bullshit and that the law's view of consent was so wrapped up in patriarchal norms that what has taken place in recent times is an actual change to the law. One compelling argument in support of this view is the death of the related antiquated views that spousal rape is an oxymoron and that men couldn't be raped. Both of these views tie rape closely to the notion of women as property and therefore that the contemporary perspective of consent is actually quite a bit different from what the law previously demanded.
However you get there, the relationship between position/conduct and what qualifies as doing what you need to do to ascertain that consent exists is fairly clear, both logically and legally. If there's a large power imbalance between the accused and the complainant, for instance, the accused is going to be held up to a higher standard if they assert that they believed that consent existed simply on the basis of the acquiescence of the victim. A sufficiently large power imbalance may (rightly) make it virtually impossible for a would-be defendant to assert that the sex was consensual, such as if the complainant was being physically endangered by the accused in some way or the sex occurred in an otherwise highly coercive environment. Similarly, if the nature of the sexual conduct changes significantly, the obligation to ensure that consent is ongoing is renewed.
Further complicating matters is that some jurisdictions permit the accused to assert their honest but mistaken belief in consent as a defence to rape, whereas some don't. It's a controversial defence, to be sure, but it's good law in a lot of places. This would allow an accused to assert, as Kobe did in his weird little letter clearly written by a lawyer, that he now acknowledges that the sex was non-consensual but he did everything he needed to do in the circumstances to ascertain that there was consent and therefore that he has no criminal liability. In places where that option is available, the defence is
not an assertion that consent didn't exist - the existence of consent is a factual question that is concerned
only with what was in the victim's mind during the encounter - but rather that the accused had behaved in such a way that indicates a clear effort to obtain consent and had consequently concluded that the sex was consensual. Indeed, an assertion of this defence actually precludes the question of consent since it relies on the accused admitting that there was no consent. For those of us that reject the notion that this defence should be available to an accused, this creates a disparity between what the law says and what we believe the law should be.