I need ideas? cause she said I will never find out?

Before I start, I don’t need any lectures. I need ideas. I am convinced my girlfriend is cheating on me but I can’t seem too catch her or find any evidence. She guards her phone like it’s the Mona Lisa. I said to her lately she had been acting like she is seeing someone else when I’m not around. She said I’m not and if I was….. you will never find out.
Like WHAT? I need to know how can I catch her? I have done all the basic Shit. I need ideas…
I need ideas? cause she said I will never find out?
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