As expected, they're both starting to get possessive of the other. Things are building up to a dramatic Christmas date where they simultaneously confess that they want to stay with each other, for real this time, probably on a ferris wheel or something.
Doesn't matter. Chasing some convoluted notion of faithfulness isn't what translation is about. In changing the title to English, it takes on a more nuanced meaning that better reflects its story. That's a good thing.
"Witch" makes sense. It's traditionally a role for women, and Ichi is unique for becoming one despite being male. The whole point is that he shouldn't be a witch, but he is. The title is communicating that.