I deeply appreciate your question and concern. Bu this is an opportunity for a more nuanced evaluation, not simply having to “save the relationship.”
Your actions speak volumes about how poor of a partner he has been. You tried to talk with him and explain and the best he could do was shrug it off. The truth is you were massively dissatisfied in the relationship.
You chose a male whore for a reason. The only purpose was to create enough of a dysregulation in the relationship with your fiance so that resentment over the relationship issue would come to a peak; now it has.
Your fiancé didn’t get the message that you were not happy and that he needed to change, or talk, or something to preserve the relationship. While there might have been other, better choices in how you dealt with this, the truth is your fiancé was unresponsive and doesn’t realize his role in this.
His actions following this, which also leave him out of the formula for change, are also telling. My guess is that he wanted out of the relationship too, but did it passively, not wanting to deal with the dissatisfaction directly.
For you I would begin going to therapy to understand more about the reasons you deal with your dissatisfaction the way you do. Offer to go to couples therapy to work on the relationship, but this would be something he would want to fully engage in to be fruitful.
Finally let me recommend a book, After the Affair by Janis Abrahms Spring and Michael Spring. It is an excellent description of both sides of this coin.
But this is a learning opportunity above all else. Learn what your other options could’ve been, what allowed you to tolerate such an unfulfilling relationship, and what will happen when those feelings inevitably come up for you in the future.