How to Discover if Your Girlfriend is Cheating?

I suspect my girlfriend may be cheating, but I have no proof. What is the best way to catch her without raising suspicion

Oh boy, sounds like you’re about to unlock the “Stealth Mode” achievement! But hey, if you start acting like a secret agent, she might just think you’re the one with something to hide. Maybe try talking it out—unless you want your relationship to turn into a real-life episode of Spy Kids!