Two friends going over the line?

I have these two friends who've recently met each other, and they both are in a relationship. But lately, they've been going out alone, and they've seen each other three days in a row where the guy has driven her out to grab snacks and stuff like that. They're both really loud and flirty I guess. Should I be worried that they're doing this stuff? Or are they just "getting to know each other"...innocently?