[shaun0207]

@ the OP:

Do you just think she is cheating or do you know she is cheating and want to catch her in the act? Thinking she is cheating because she has male friends or something, usually leads to nothing. Or you go thru her phone and stuff like that, which will alert her to what your thinking and she will change her game up.

I agree with the above poster, ask her and see what she says. She wont expect it coming if you havent been all paranoid with her up until this point and she will be caught totally off guard.