[Acheron]

Nothing wrong with it at all. There's no reasonable assumption of monogamy if you're only dating, so morally you don't even need to tell them that you're seeing other people. It isn't any kind of relationship until you both say so, and if you aren't in a relationship then seeing other people isn't cheating. However, while not exactly cheating, I think it'd be wrong to continue seeing other people if one girl starts calling your her boyfriend and you don't correct her. While it'd be partly her own fault for assuming too much, you'd be deceiving her.