I have this headcanon that at some point in hogwarts ( year five or something ) remus and sirius just knew eachother’s feelings and had an unspoken arrangement not to do anything about it for all the usual reasons ( insecurities, fear for their friendship… ) but at some point during year 6 they couldn’t do it anymore and they finally got together. for the same reasons than above they didn’t tell the others about it and kept it a secret. and then the prank happened and as remus is being comforted by james and peter he tells them that they were in a relationship. suddently james and peter understand how much remus trusted padfoot and how much the prank hurted him.
when remus forgave sirius, he kissed him in the middle of the great hall.