Marco is not oblivious, this really is a case of Star digging her own grave, he actually excuse himself for Jackie and went to Star to see what was going on, he knows she is upset about them, and ask her if is okay if he and Jackie hook up. That is Marco giving Star a way out, and Star doesn't go for it. Also lets not forget in Season 1 Star made Marco very clear that she was not a potential love interest for him (remember the Red Moon Ball). So no this is Star rekting herself