They met at an underground concert/pub some years before bandersnatch (1984), and what actually drew them together and made them start really talking was on the "second" repetition of events when Kitty asked him if they have met before.

Which links to my other headcanon that Kitty isn't 'fully aware' of the loops and timeline shifts like Colin or Stefan, but she notices or at least feels when something is happening more than most people, being one of the reasons that made Colin like her.

One of the other reasons is that she grounds him a lot. In many ways.

For example, I think Colin tends to neglect his basic needs a little like sleeping and eating both because he became so detached of the life/death conception after experiencing it so many times that he doesn't bother much now, and because sometimes he becomes so immersed in game-developing he just forgets about everything else. And Kitty often pops his bubble to tell him that cigarettes and black coffee is not breakfast and his genius brain will stop working if he keeps sleeping two-three hours a day.

And this would truly be a bother if it was the remaining 99% of the world population, but since it's her he doesn't mind it much. He gets a little stubborn sometimes at first but ends up complying to it.

Another thing is when he dissociates himself too much or gets too nihilistic or freaked out and Kitty helps him clear his mind and get his head back in place. Pearl also does this job on herself too sometimes.

Also related to this, she doesn't like it much when he mindlessly puts himself at risk (or straight up k words himself) even though she "knows" he will comeback, both for emotional reasons and because she doesn't want him to end up "in the hole".

Now leaving out the existentialistic depressing stuff, they loove to get high together.

Kitty does it less than Colin because yk Pearl (and also she scolds him when he's getting loaded way too much and ends up neglecting some affairs or not watching over Pearl properly) but overall they often trip together.

Overall they have a very similar music taste and like to attend underground/alternative music events and places.

They are obviously non-monogamous, or at least have an open relationship. Kitty relates to other people more than Colin since he doesn't connect very easily (and she isn't an ass like him).

Kitty to me has abstract/expressionist artist vibes, and their flat has some frames of her paintings on the walls. She also helps Colin with design ideas and visual concepts for his games.

I like to think Colin has a lot of money from his profit saved for Kitty and Pearl, in case anything happens and he disappears completely without returning, they won't be left with nothing.

Talking about Pearl, she wasn't exactly planned but she was not unwelcomed either when Kitty found out about her pregnancy. They had a serious conversation about it and took a decision based on what they both wanted. I feel like Colin mostly allowed Kitty to decide if she wanted to have her or not and he would just go along with whatever she wished to do. But they both love her and are happy to have her.