Confused. My Wife Starts Seeing Another Man, But Told Me Yesterday She Wants Me Back...

Ok, so all I have to say is, what the hell just happened?  My wife calls me up yesterday asking me if I can watch her daughter because she needs to go somewhere to submit an application.  So, I watch her daughter for an hour 1/2 and she finally comes back to my apartment.  She and I are talking about nothing and she notices a note on my refridgerator (from an x-girlfriend that has been helping me through this separation).  The note clearly states that she appreciates having me back as a friend, etc...  My wife, mind you, who has been seeing another man (on top of that she got with him a week after we split), gets pissed and starts throwing a fit.  I take her outside of my apartment and start telling her she was the one that threw me out and started seeing another man almost immediately after this happened.  She then had the nerve to tell me that she had come over to also tell me that there was a chance she wanted to work this out with me, but now that chance was gone because of the note.  My ex-girlfriend was the reason, my wife, says we split up.  My ex and I were friends, and I had never done anything with her behind my wife's back.  I made the mistake of hiding it from her, because when she knew we were talking or she was contacting me, my wife would blow up on me, so I kept it from her to avoid conflict.  Anyways, so she tells me that there was a chance we could work this out, but it's gone now because of the note that clearly states my ex's stance on how good a friend I am.  I don't understand how my wife could get mad, she's sleeping with another man, and then thinks she can just come back to me when she pleases to take me back.  She should be greatful that I am even talking to her and haven't hired a lawyer to hit her with adultery.  Does she want to mend our marriage or was it just a ploy to try to hurt my feelings because she saw the note?  We talked afterwards and she got over it.  Now she's acting like she was last night before she saw the note.  Does she want me back?  Should I even waste my time hoping?  Don't know what to do?