It had been twelve years and Remus still hadn’t come to terms with what Sirius had done. He still couldn’t believe that one of his best friends had committed such an atrocity. Yet in those twelve years he had come to terms with his feelings for Sirius. He was in love with him. He had been in love with him from the moment that he suggested that he, James, and Peter all learn to become Animagi so that Remus wouldn’t have to go through his ordeal alone. He would scoff at himself whenever he thought of Sirius and his feelings for him. Great timing Remus, he would think, just twelve or so years too late in the realization of your feelings.
In those twelve years he also hadn’t seen Harry Potter more than twice, and both those times from afar. He harbored too much resentment towards the boy. It was ridiculous, unfounded resentment, but it was still there. So when Dumbledore had offered him a jog as Defense Against the Dark Arts professor, Remus had been more than a little bit cautious. He had all sorts of reasons to turn down the job (he was a werewolf, parents would have Dumbledore’s head if they found out, how was he supposed to control himself?), but he accepted the job, the pull of his childhood home was far too great.
It was there that he met Harry Potter, the wonderful, broken, Boy Who Lived. After defending the boy from a dementor attack on the train to school, any resentment that Remus harbored for the boy vanished. And in it’s place was a strong urge to keep the boy safe.