<human>: Can you condense the text into a few key points?

We've been dating for about 8 months. Let me preface this by saying that there is so much I like about this girl. She's sweet, caring, and adorable. I really was starting to see the possibility of a life with her. 

On to the issue however... There was one instance where she was texting her ex a while back, she was open and honest about it, I told her it bothered me, and it hasn't been an issue since. Fast forward a few months, things have been really good between us. She had a lot of work stress as she had just started a new job as a kindergarten teacher, but I've really tried to help her work through it and be there for her. She is so much less overwhelmed than she used to be, and our relationship has been better because of that. 

Now I recently found this random t shirt by her bed, which I thought was odd because it was a medium, she wears a small. I asked her about it, she says Oh it's no big deal it's just a shirt I wear to bed every once in a while. Ok whatever, I get that. Fast forward to today though, I have a ton of time on my hands and I start looking at old photos on Facebook, and I see the shirt.. On her ex. It's her ex's shirt. Presumably she's keeping it beside her when she sleeps?

I feel like she can't let this guy go. She has told me that they dated for 6 years off and on. I was in a relationship like that myself, but the girl went on to get married. I know how addictive those relationships can be. I've told her that and that I worry about her going back to him or not being able to move on. 

What do I do in this situation? I really care about this girl. I've put so much more of myself into this relationship than I have with any in the past. I'm lost. I feel like she feels the same about me, but why would she be hanging on to his stuff? 

Please. Need advice. She doesn't know that I know yet, I need to know how to approach this situation.
<bot>: gf keeps ex's t shirt by her bed, lied to me about it and said it was hers. What do I do?