Kitty > Chekov 1 of 2
She likes this guy soooooooooooooo much. He's basically exactly what she needs in her life. If a doctor was writing her a prescription it would be for at least twenty of him.
He's extremely smart which she really connects to well being a genius in her own right. Normally, that results in her connecting better to older people, but since he's a genius too he gets to be about the same age! She doesn't get bored hearing about technical stuff, she gets into it even if life experiences have kind of trained her away from rambling about it herself.
He's fun. Even when he's at his deepest and darkest he feels like a breath of fresh air somehow. She finds it easy to be with him and easy to enjoy herself. It makes her feel—I would say younger, but let's be real, more like her actual age instead of always acting older.
He's extremely sweet. And since she's gone from downward spiral to evening out somewhere in the low regions full of self doubt and regrets and insecurities and self disgust there are times just hearing that he likes being with her really elevates her. And he's great about just putting the happy words out there like it's nothing. She tends to hold those things in. There was always a protective wall before Marina. Reid (with some help from Allen and others) broke that wall down and left her feeling vulnerable and exposed and not always knowing how to let that show. So, she probably doesn't tell or show him as much, but every kind word and compliment has been very powerful for her at a time when she needs them most.
He's very physically affectionate. And this is where things can also get confusing. First of all, he looks like Nathan who we've already covered is like a student and pushing up against surrogate son (and second chance). Now, at this point in their relationship they look VERY different to her because of their personalities. But she knows logically that they are nearly identical and sometimes there's a curve of the lips or an angle or a look and it is momentarily disturbing. How can it not be, right? Still, this is largely superficial if not for the part where she'd be concerned it would cause issues for Nathan. He's not the most stable, did you know? And she is very protective of him. Next, there's Chekov's accent. Now, his voice and Piotr's are extremely different, but when she isn't exactly exposed to a wealth of men with Russian accents there are times when it can be very haunting to be reminded of your ex-husband who accidentally murdered you. We also have the issue we've already talked about some, but for anyone else who may be reading, Kitty has a tendency to become easily touch-starved. She wants/needs physical affection, but she's not one to seek it out except in a relationship which she isn't in and hasn't been for a couple of IC months now. It makes every little touch meaningful and a little confusing as she wants more, but is also wary of it.