Ron could transfigure himself into a chipmunk, which was not, as Remus went, terribly useful. He was a very nicely colored chipmunk, Remus informed him, nonetheless, a chipmunk just didn't have much to offer a werewolf, and Ron vaguely suspected that small creatures scurrying about reminded Remus of Peter, in any case.
As such, he wasn't much use during transfigurations when Harry, who was a lion--of course he was--would just come over and run Remus until he cried "uncle". Or, since he was a werewolf at that time, rolled on the ground and whimpered.
The part Ron was good at--and he was quite good--was making Remus laugh on the following days, when muscles that were worn just from the everyday experience of living screamed at Remus about how he could do such a thing to them, and everything else in his body was considerably less kind. Ron could always, always make Remus laugh, even on the worst of days: days when the pain was about loss rather than transformation.
It was only fair, only fair that Ron be able to find Remus inside of himself, pull him a little toward the warmth, because Remus more often than not gave Ron the world in tiny ways, little ways that nobody else would think to. For instance, he was able to interest Ron in astrology by starting with stories, rather than charts and maps. He was able to coax wandless magic out of Ron by distracting him from thinking about the process so much as the results.
Remus knew how to find the best parts of Ron, and Ron knew how to find Remus beneath his pain and if they didn't work for any other reason, they would work for that one.
Of course, there was also the fact that the first time Remus kissed him, hesitant and clearly a little drunk, he'd tasted of cinnamon shortbread and clotted cream and his tongue had been the most brilliant thing Ron had ever felt in his life. That didn't hurt either. Or, that when Remus had pulled away and said, "Sorry, sorry, terribly inappropriate of me," and Ron had ignored all of that and pulled him back and kissed him hard that Remus hadn't held back, hadn't acted like Ron might not be man enough to take it, like maybe he'd best find Harry if he wanted someone of that caliber.
Remus always met Ron halfway and was more than willing to push him over the edge.
It would have been rude of Ron not to be willing to return the favor.
His mum had raised him better than that.