Suggest a romance novel where the leads are in love and everyone knows except them

I have read mangas with this plot but I have rarely encountered book like this. I enjoy it because of the pining, as I get bored when they finally get on with the relationship. I really like it when they're obviously into each other and everyone knows this, but they are unaware of their feelings since they feel it's a normal thing. The thing I like the most is that they're closer to each other than to other people yet they think it's no biggie or have just grown used to it. It doesn't have to be heterosexual romance, btw.
* Friends to lovers
* Slow romance
* Know the other person to the T