I think her closest relationships are going to be with Aquaman and Superman. Romantic or otherwise who's to say, but I think a bond exists in both cases and Steve is threatened by it.
I say that because I thought there was some deliberate tension in the art and the writing in #7 when it came to Steve's communication with the league. He talks to everyone in turn except Aquaman and Superman, with cold glances being thrown, and to boot hinting at an uncomfortable silence by Barry swooping in to say something. Thus I get the feeling Steve doesn't like those two very much. And considering he's in love with Diana, jealousy would be the most likely reason.