the song is a classic. as it's been pointed out numerous times, not only wasn't the song ever "rapey", but was actually empowerment for females of the era.
people ignoring the context simply to make it out to be rapey and get up in arms about it are a part of the problem, not the solution. I mean this isn't even comparable to previous past terrible norms in pop culture like black face, misogyny, native Americans and asians in golden age of cinema, etc.
in today's metoo climate there is definitely something to talk about in regards to the song.. but it being "offensive" isn't one of those things. if anything this song is one of the million building blocks that have built up to modern feminism.
tl;dr, an unwed dude and chick just hooked up, she's expected to leave because "it's not proper", despite wanting to stay. he's basically saying "screw what people think".
she says no because, no matter how much she wanted to, it was WILDLY inappropriate in social norms for her to stay.