Suspicion lead to snooping... Likely break up-but there's a twist.

My first post here, I am looking for suggestions/support. A little background on my family and myself. I am 24, my (likely to be ex) girlfriend is 23, we have been together almost six years, have a four year old daughter and a son who passed away shortly after birth last February. Okay. Roughly a year into our relationship, I had found out she had cheated on me, (early 2010). That was the first time I had experienced it, and we were living together already. I went through A LOT of mental pain (you know if you've been in the situation). I forgave her, she got pregnant and life went on...

Fast forward to these last few months. She has been sitting up stairs in our room doing homework (which I don't doubt); a lot of her time is spent sitting on our bed. I had noticed this and became suspicious, as she has mentioned she's depressed also, that I don't act the same, that I don't act like I care about her and so on. Just out of suspicion, I looked through her phone. Ever since she cheated, I've kept my guard up; in all reality we shouldn't be together but I am doing my best for my daughter. On her phone was a messaging app called KIK. I am familiar with this app since I had noticed my manager using this on his phone to message another girl; and he's a married man. I know some of her passwords, and managed to guess it. There was a message from someone she plays Xbox with asking if she'd be getting on today. I left for work and confronted her through texts (this is where I made a mistake, I should have monitored the app until I had solid evidence).

We went back and forth through texts, she got VERY defensive, "we're done!","this is like living with my parents!"... Later that night when I got home, we got into it. She had changed her KIK password, and WOULD NOT tell me what it was because "I don't need to monitor like a child". Which I agree with. A few hours of yelling we were able to talk it out, and I felt like I had just overreacted. I should add now that she said she installed the app to talk to her sister who lives in England. She SWORE up and down that she only messaged that guy because they played Xbox together. Which is fine. The next night while I'm at work, she drops off a bag full of candy and a new Xbox game she knew I wanted, and a card apologizing for arguing. She still denies that she was talking to anyone other than this one guy, and that they had only talked about when they would be online. She deleted the App, deactivated her Facebook and changed that password aswell. I asked her recently what her Kik password was and now she can't remember...

A few weeks go by, until tonight. Just out of curiosity, I checked to see if she had installed the app on her phone again. It wasn't there, but had been installed again on 11/22. I found this through a file explorer program, Kik had left a trail of temporary files. I asked her recently what her Kik password was and now she can't remember... Obviously a lie. She had also installed Whatsapp which is another messaging app, and under the Google Playstore she had searches for "messaging apps". I also found a screen shot of a Kik username, which read "Add me on KIK" followed by a username. I work night shifts, and she had installed these apps last Saturday while I was at work. So, I know for a fact that she has installed these with intentions to use them (even though she said she didn't need it on her phone and couldn't remember the password.) I just can't pull together any hard evidence that she is talking to another guy. I cannot for the life of me guess her password.

I have a lot on my mind and I'm having a hard time organizing this. Now I want to make it clear I have been in NO WAY controlling over her. I am not crazy. I know it looks like I'm losing it trying to crack passwords and all but there is a serious twist, which is why I want clear cut evidence before I confront her. She has threatened suicide before. We have a four year old. She mentioned in a text sometimes she feels like she wants to wreck her car into a tree... Cheating or not, I don't want her to do that for my daughters sake. And I honestly feel like if I move forward with initiating a separation, she may very well try something dumb. I have pretty much accepted at this point she is up to something. Which makes me feel like a fool for trying to work it out years ago.

Now, I have family local to me, her's are in Texas (we're in Virginia). I have NO idea how to end this when I finally find solid proof. Tell her parents? My dad will be retired come the new year, so I can drop off my daughter to make sure she is safe. But pretending like I don't know she's doing something, kissing her... I have been losing sleep about this since the beginning of November (since I first found the Kik App). I am really trying to protect my daughter from harm ( I don't think she'd hurt her) and make sure she doesn't lose her mom. Mine passed away when I was ten, I don't want my daughter going through that. I'm really trying to keep it together.