Is my girlfriend a potential cheater?

Sooo, my girlfriend is one of those that cheated on her last boyfriend and was... promiscuous, before we started dating, so naturally she still has a lot of guys calling her up or texting her tryin to get a piece. I have seen it, and she has always said hell no to them, and she tells me she loves me and thinks we'll be together forever... I believe she thinks that, sometimes. But jst recently I have had a couple doubts about her faithfulness, not really that she cheated, but she might be thinking about it. The other day she was looking through my cell phone... she's not very trusting of me... even though she was the one who cheated before, and I grabbed hers and started lookin through it, she grabbed it out of my hands and quickly deleted a text she sent to some guy... i didn't get to read it and she told me it was nothing... but she made a big deal about it when I was about to see it, so I doubt it. There are other things too, but not enough to space to say them. Anything to worry?