So, I've been having casual sex with this guy for just over 4 years. It had never occurred to me before but I have never ever turned down his request to hook up. Even if that meant rearranging minor plans (like postponing hair wash day, something like that). The sex really is just that good. 
2 weeks ago I came down with this brutal cold that's going about so when he messaged saying "thinking of coming round on Wednesday", I said I had to postpone.
No word of a lie, he has text me every day since then. Asking how I'm feeling, how my week is going, general chit chat. Normally he would only text twice a week at most, and one of those would be arranging to meet.
At first I thought he's just gauging how I'm feeling so he knows when we can hook up again but he's been messaging on days when I know he's out of town so wouldn't even be available to meet.
On Saturday night, we messaged for hours, and he's asked if I want to go out for Christmas drinks once I'm fully recovered... something we've never done in these 4 years.
This is not a Hallmark friends-to-lovers story because neither of us are looking to pursue a real relationship with the other, but it's definitely got me thinking that playing "hard to get" even unintentionally really does work!