I don't trust my girlfriend.?

Hi! I've been going out with my girlfriend for about a year now, and shes great, But once I went overseas for about a month and came during our 8th month, she seemed like a completely different person. One of her friends told me that see has been flirting via text message with a excessive amount of guys, and at first at didn't believe it. I then confronted her amount it, and she wouldn't let me see her cell phone text messages because she said they were private. Then about a week later, I ask her again and she was even more possessive over the phone and quickly ran to the bathroom to because she said, "I feel sick." When she came back, she allowed me to look through her phone and there wasn't a single text message in the Inbox. I told myself enough is enough and got into a argument with her, and she later told me that the reason she cleared her inbox was because she didn't want me to see the messages in her Inbox, because she was sending one of her male friends a gift basket because he is away at camp. She later tells me a week after that shes walked with this guy at 12am until 2:30am through the neighborhood and a local park, but she swore that she didn't cheat on me. Then, 2 months after this occasion I tell her that she either lets me see her text messages, or we will break up. She lets me read them. She has messages from more than 5 guys where she is calling them baby, boo, and honey. She doesn't even answer my text messages with these names. (But before the my trip she always would let me look through her phone at there was not one flirty message ever!) In one instance she even says I love you to a guy. I of course, reacted because I have not once refereed to a girl in that name and style, But after this occasion I was no saint myself. I became overly friendly with another girl and my girlfriend soon finds out from reading my call long. She started to cry and call this woman to come to my house so we three can have a discussion about this. I didn't cheat with my girlfriend with this other girl, all I did was flirt. No walks through the neighborhood no nothing. Me and my girlfriend end up getting back together. Although, I wasn't the ideal boyfriend, I seem to believe that she is the one at fault throughout the problems that occurred after I gotten back from my trip, and also I don't trust her. What can I possibly do to trust her again? What measures should she take to become the girlfriend she once was? please help!
--------------------
Then dump the *****. Next question.
Source