However you need to do it right.
First, you need proof that she is lying.
Maybe you spied on her and checked her email or cell phone.
This means that you have real proof, not just feelings.
If all you have are vague feelings, you can't confront her. It won't work.
Once you have gathered solid proofs, you need to realize as well that you spied on her.
She will accuse you of not trusting her.
The next step is to choose the right timing and attitude for that.
You don't want to point your finger at her and tell her how bad she is.
You want to sit down and have an open dialogue about what is going in your relationship.
My guess is that you still care and that you still want her.
If it is the case, the goal is to empower your relationship, not to find someone to blame.
Say something like: "I face a challenge with our relationship and I need your help to solve this dilemma. When is a good time to talk about this?"
If she accuses you of spying on her, you can say:
"Yes! We both did something which betrays the trust in our relationship. We are both guilty. Now, what are we going to do about it?"
If she says:
"First, I need you to promise me that you won't do that again..."
You can say:
"If I have serious reasons to believe that you are cheating on me, I will use any tool I can to find out what is truly going on."
"Now, my turn. You cheated on me. How do you feel about what happened?"
The best way to go is: no demand and no pressure.
The first step is to get a feel of what is truly going on in her mind.
For the full story and what to do next, check the jealousy e-book and MP3 audios at:
http://vitalcoaching.com/malejealousy.htm
Enjoy!
vitalcoach