I think one of the incredible components of Killing Eve is not just that Eve is getting darker or that Villanelle is getting softer... It’s that, on a characteristic level, they are both moving towards one another. Villanelle has, in the first season especially, established herself as emotionally detached (both due to her line of ‘work’ and her psychopathy) excluding a few moments whenever Eve is involved (even her relationship with Konstantin is only one of circumstance). Eve, in the first season, was introduced as a character with an unacknowledged brilliance and was quite a bit more reserved, both in her work and with her husband, than she has been in this second season.
But it’s in season two, namely the latest episode ‘Desperate Times’ that has really revealed, in an almost tangible way, that these women are so attuned to one another that they are changing themselves from thousands of kilometres away from the other. Eve is, allegedly, stood firmly on the right-hand side of this spectrum of darkness (where she is a good wife and a good worker and does not fiddle with knives or stab people and is conflicted by wearing gifts she has received from a known assassin). Villanelle is, contrarily, stood firmly of the left-side (where she does not feel remorse, does not express genuine emotion and does not think twice about killing someone to suit her own agenda). But during the second season, we the viewers are privy to the delicate shuffle both are making closer to the centre of the spectrum; Eve away from the right, and Villanelle away from the left.
Eve is embracing her obsession, she is becoming more detached from her husband, she grows more restless in her marriage where before she found at least some contentment. Villanelle is more and more desperate for Eve’s attention, she is more genuinely emotional than we have ever seen her, enough so that she openly weeps and stares at herself as she does so, and finds some hopeful joy at the end of it. She cries for her genuine pain in not seeing Eve, being so far away from someone that she, in an admittedly twisted way, loves.
So, yes, I think these two characters are metamorphosing before our eyes, but no, I don’t think that Eve is simply growing dark, or Villanelle is simply getting softer. I think they are, episode by episode, becoming like each other. And if that is not an indication of mutual love (or at least obsession), then I’m not sure what is.