Hey Sarah! Awesome to see you and Oliver here! I've got some head!canon for Oliver & Percy, so why don't I throw some of it out and you tell me what sticks for you and your Olli?
Oliver was lucky enough to see Percy without his younger siblings around for 2 years, so he saw the somewhat lighter and "capable of being casual on occasion" side of Percy. They may have bonded over quidditch (Percy's cheered for Puddlemere since he was young, but never too vocally around the Burrow - one of many things he tended to keep to himself). And yeah, seeing each other day after day at school.
Especially after reading Oliver's bio, I have this image of Percy one day sitting him down and going "Oliver, we need to talk about your grades because I don't want to take the risk of them not letting you play anymore because you're the best keeper we have. Now, if you like, we can institute a study regimen that would compliment your training regimen to allow you maximum time for flying, schoolwork, and yes, personal time as well because I know that's important to you and I wouldn't have you do otherwise..."
I sense they sort of drifter apart in the immediate years after school, especially with the break in the WEasley family, but maybe reconnected after the battle? Percy would have appreciated seeing Oliver there at the funeral, for sure. And I think he wouldn't have anyone else show his daughter how to fly a broom :D