Does anyone know how to find out if your girlfriend is cheating on you with out finding her doing it

Wouldn't that be like trying to prove a negative?

If she isn't doing anything, what do you expect to find?

The signals are always there if you can read or se them .If she always come home late,if she always go out with her so called friends every weekend,if she always go into hiding to answer a phone called and lastly if always tell you that she is so tired whenever you want to have sex with her.