Honestly, despite me liking their relationship, its clearly unstable as fuck and not perfect. Her saying that they should move together after only a few months of dating, and when they're teens at that, is a huge red fucking flag that can't be ignored. Not to mention her being extremely insecure and jealous of a girl she hasn't meet is not a good thing. If, in chapter 29 Yami and Yuu are still together, then it all but means that they were dating throughout the first arc, up until before chapter 19.