<human>: Condense the text into a few key points

Okay so I dated this girl for over a year , she's my first love , my sun and stars and mostly my best friend. Our relationship was next to perfect except for that a few months back I caught her Instagram DMing some other guy , and she said it was nothing but it turned out her and the guy had been "friends" for most of the second half of our relationship behind my back because she knew I didnt like him. 

The only reason I wasnt completely destroyed about the friends thing was because she doesnt really have any close friends other than me so she must have been lonely and she swears they were nothing but friends . But I found out they even planned a date she said yes to but couldn't follow through with. 

She wanted to prove herself to me after we broke up by blocking him on her accounts , but she couldnt block him on one of them for some reason. I suggested as a joke that she talk to him and get it all out of her system before we try anything again but to my surprise she jumped at it. She seems so excited and I cant even stop her now , but to prove herself she wants to have an open relationship with me and tell me everything that happens between them . 

I just don't know how to feel about this ... would it be wise to wait it out in this open relationship? Ill be talking to other people too i just don't know if i'm getting my hopes up with her because I really believe we do love eachother.. we planned to get married. Is it likely she might be actually stolen from me forever? I could just use any advice really . Thanks.
<bot>: My ex wants to get another guy out of her system by pursuing him , idk how to feel. Does this open relationship sound worth it? Should I see where this goes?