James and Regulus falling in love with each other before Regulus finally ran away to the Potters because Sirius talked about the other so often that it felt like they knew each other their whole lives and not just from passing in the halls. When Regulus and James finally began having genuine conversations and not just shy hellos where Sirius hovered nearby, they were both quickly aware of how they felt for one another but both so scared that the other didnt like them back but it was so obvious to everyone else how they felt.
It was obvious because Regulus would go from quiet to rambling on about everything and nothing and James would go from constant chatter to absolute silence just listening to him and nodding along with so much enthusiasm. It was obvious because James made Regulus smile over the smallest things and Regulus would make James fidgety. It was obvious because James hated coffee but pretended to like it just so he could drink coffee in silence with Regulus in the early mornings. It was obvious because Regulus hated physical touch unless he was the one to initiate but he blushed every time James would accidentally brush up against him, or purposely grab his hand for whatever reason, or cuddle next to him during movie nights. It was so obvious.
It took a talking from Monty for Regulus to realize that James reciprocated his feelings and it took a very shy kiss from Regulus for James to realize that Regulus wanted him back.
