I like to think that when James found out he fancied Reg he didn't pull some dramatic ask out or serenade him on top of the Gryffindor table. He kept it quiet and showed love through actions whether it be on purpose or not. Loving is a second nature to James so whether he wants to keep his crush quiet or not he just can't.
When someone found out James had a crush on Reg they immediately went to warn him of whatever James future plans could be. And when it never came Reg started to wonder if James truly liked him at all.