Devils advocate here....
It doesn't sound like she is ready to live poly from the definition generally used in this site, as in honest, open communication and commitment to working on ones own issues as much as the relationships.
I know I really don't have enough info to be saying some of this but the past history of cheating and the not discussing growing feelings for someone who may end up living under the same roof as the two of you?! Major red flags.
Even if you chose to move on to another mono relationship, I urge you to read some of the threads about being your own primary...I think this concept would do so well for anyone, mono, poly, straight, gay, tall, short, etc.
Wishing you well.