<human>: Can you provide a brief rundown of the text in within 3 sentences?

Sorry if there are mistakes, I'm on my phone. So anyway, I've been talking to this girl (let's call her Michelle) for about a month or so now, and everything has been going pretty well. We've been going on dates frequently, we have no problens having conversations while we're out... but I don't trust her. I know I have trust issues of my own but I'm usually all for trusting someone until they give me a reason not to. Anyway on to the incident. 

So when me and Michelle first started talking, she mentioned her ex boyfriend who was apparently a huge dick to her (emotionally and physically abusive she says). Anyway she spoke so low of him over the course of a week or so, of how much she hated him and never wanted to speak to him again. Well one day we were walking around in our downtown area after getting lunch and we pass by a store where she sees her ex in. Me, not really giving a fuck keep walking, but she says "Oh, shit" and walks faster. Well he comes out and calls her name and he hugs her (she doesn't really reciprocate) and we say an awkward hey and continue walking.

Well he comes running back out and stops me, and says "Hey man I just want to let you know, that a few days ago, she texted me and came over and we had sex." I tell him thanks for telling me and we go home not speaking. I decide to forgive her because we aren't dating officially and I know if a girl was wanting to have sex with me I would've done it, so I can't be a hypocrite.

It's not really the sex that bothers me, it's the lying that she hated him so much and still did it and in the time of us not texting or whatever, now all I can imagine is her doing the same thing again. She kept the ex thing hidden from me, so who's to say she won't do it again. I know she's young but I do want this to work but I feel like she would cheat on me in the future. So what should I do? Thanks for reading this novel and any advice you guys give.
<bot>: Girl I've been talking to, easily hid a secret from me about sleeping with her ex and now I don't trust her.