Re: Found explicit text messages in fiance's old phone.....
Get to rejection quickly. Don't waste your valuable time on a poor prospect. She has proven she has the capability to cheat, and she has proven she will shift the blame onto you. There is nothing in what she has said or done which indicates she understands how wrong it was to do what she did. There is good reason to believe she could have cheated many times already but you just have not detected it.
If you were looking to buy something expensive and it had that kind of bad history you would not buy it. The risk of failure is high with this one.
You could choose to spend more years with her and hope it works out ok. Those would be years of your life you can never get back.
Your choice. Cut your losses now and move on to a better life, or stay with this one while hoping she doesn't cheat again.