It only took 30 days
Day 1
Remus noticed that Sirius always always bit the inside of his cheek whenever he was working on charms as it was his worst subject. Remus thought it was cute.
Day 2
Today Sirius noticed that whenever James, Peter, or himself mentioned Remus' furry-little-problem Remus smirked. He found it cute.
Day3
Not that he would ever actually admit it but Remus found that Sirius was at his happiest during potions class.
Day4
Sirius absentmindedly noted that Remus had a habit of humming a strange song whenever he walked to or from the library and when asked him to sing it he only blushed.
Day5
As the full moon was the night before Remus noticed that the dog Sirius tended to be much more cuddly. Remus would never say how happy that made him.
Day6
Sirius noticed that during history of magic Remus doodles on the margins of his notes.
Day7
Remus noticed that during history of magic Sirius doodled people. Today it was himself, it was a strange thing to keep secret though as Sirius was very good at it.
Day8
Today Sirius decided enough was enough he was done with the Hogwarts girls they constantly complaining that he was "to friend oriented."
Day9
Remus noticed that Sirius had stopped dating the girls of hogwarts not that he would ever admit it but he was happy about that.
Day 10
Today Sirius noticed that Remus seemed much happier now that he wasn't dating. Sirius was very proud that he was making his furry-little-friend happy.