Talking to her about it would be the smartest, most logical, thing to do. Just hoping that it's a misunderstanding won't work because whether she's cheating on you would always be on the back of your mind, and it's stupid to just break up with someone with no valid reason.
Asking about a moreway is no good, not until you learn what she's into (all the more reason to talk to her).
Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you. - Friedrich Nietzsche