Keep digging. I am sure this relationship went physical. Install a key logged on computer and spyware on her phone. Did she admit to the physical part? She is only confessing to what you know. I think this is the tip of the iceberg

I know you want to believe in your wife and mother of your 2 year old. It's hard to face reality that your wife, the one you trust, depend on and believe in has been lying to you and worse yet sleeping with another man. Here is the bottom line facts:

1. She not only lied to you but has been lying for months to you. Looking at you pretending that all is well. 

2. She knew you were not comfortable with the text messages and you asked her to stop. She deceived you and went against your wishes because she was thinking about herself. 

3. She did not come to you and confess, she tried hiding her actions by locking her phone. You had to investigate. 

She will never transparent and truthful. Maybe she will promise and change for a short time to keep you but she will always chase that feeling and be a liar. Don't be surprised or fool yourself in thinking they were only hanging out and talking. If you absolutely need the truth hire a investigator to give her a polygraph test. You might just find out all you need once she knows your actually persuing this test. 

Goodluck