The very first words Missy uses to describe the Doctor in any way are “my boyfriend.”
40 plus years of characterization and built up history and subtext and friendship/hatred/need, all at best skirting around the idea that they could be something more.
But it isn’t until the Master is played by a woman that the subtext becomes text. Doctor/Master is my OTP, but this is not how I wanted it to become canon. It reeks of heteronormativity and misogyny. I much would’ve preferred Missy to have the same subtextual relationship with the Doctor; no forced kissing, no “boyfriend”, no “two hearts…and both of them yours”, just subtlety and sniping and “I’m going to destroy/take over the Earth, possibly to get your attention, but no it’s cuz I’m evil, but please pay attention to me” and “I want to stop you but I can’t kill you for reasons.”