my opinion on canonical Elliot and Leo is that Elliot has a crush on Leo. a) we see it in how enthusiastically protective he is of him, b) he awkwardly tries to impress Leo with the song and the bookmark, c) the tea party scene. Leo clearly loves Elliot, but his feelings moved beyond a crush by the time Elliot asked him to work for him. They’re in some kind of liminal relationship during the series, more than friends but not necessarily dating. Both of them value that, but it’s Leo who treats it as a steady relationship and Elliot who still gets nervous and excited about it