I would work on your relationship and possible trust issues first (I would have trust issues anyway). Nothing will tear apart a flawed relationship faster than complicating it with new partners and situations. Her rushing you into this isn't fair. If she cared about your feelings, it seems she would go at your pace, no matter how much she wants other people. Is she claiming "poly" to escape from issues in your own relationship? (I ask, because I have done this exact same thing) I believe heartily in the idea of polyamory, but have found, that each person has to want it, not just accept it, but whole heartily want to do this.
Also, she cheated on you! Ugh, sorry, I am just disgusted for you on that one. And you "cheating" on her, with her permission doesn't count as cheating. Oh and kudos for reading up on the topic, it sounds like you really love her and are trying very hard to make this work. Make sure she is making an effort for you as well.
Have courage to continue this journey, for it holds nothing but lessons and wonders.