This girl texts me and flirts with me all the time (specifically me), but then she always keeps her physical distance. Would it be reasonable to suspect that she's seeing another guy, intimately? She claims she's single.
I assume all single women are seeing multiple men at any given time in the same way that single guys are going after a few different women at any given time. Don't worry about what they're doing. If you're the best suitor, what those other guys do won't matter.