I have had suspicions about these two since the word go of Infiltrator, when Kid Flash did not make an advance on Artemis. I thought it was a bit suspicious, and ever since, I have suspicioned it even more. Especially when this image came to light. The episode this image has come from is entitled Bereft, and aires tonight, so I am eager to see what happens. The summary of the episode states that the entire team loses their memory, and I have watched a clip of the episode, in which Miss Martian mistakens Superboy for Superman, not remembering ever meeting Superboy. So perhaps the two (Artemis and Kid Flash) have a little relationship in the episode, then forget what happened in the episode after their memories are restored, and throughout the series, they begin to get closer and closer, but never actually become "a couple".
Then in the long term, I suspect in the series finale, Artemis is killed, and as she dies, both of them have a "moment", and reveal their feelings to each other. Which is a shame really, because ever since the Young Justice Poster I have been looking forward to seeing Artemis, and I hope she doesn't die. But she does seem to have a connection to Cheshire and possibly even the Light. What do you think?