While I admire your ability to take the "high road" and control any outward display of anger or resentment, I'm not sure if that's not the reason why you're struggling.
You ARE a good person, but you're human too. It's a natural reaction to become angry when the person who you trusted most, stabs you in the back. It's normal, if not right, to be angry when there is injustice.
If we all took the "high road" and let our respective cheaters "off pretty easy," then don't you think society as a whole would start to feel that infidelity is not that terrible? It's bad enough that movies and tv often display cheating in a glamorous light. It doesn't show the realm of destruction it inflicts on the betrayed spouse and innocent children.
When something unfair occurs, I think anger is appropriate. It shows that we as a society know this to be morally wrong.
I'm not saying we should go to the extreme with anger and resentment, although I certainly understand those feelings. I'm saying a certain amount of justified anger and expressing that anger is good.
You're stifling a normal response. You may also be stifling anger and resentment because your high road behavior isn't working at making him remorseful. You say that you've stopped hoping for that, yet you continue to rehearse in your brain your answers if he should ask for another chance.
Don't get me wrong. I get where you're coming from. I often stifle my anger to get what I want from STBXWH, but I also allow myself to lob an insult occasionally when I think he's forgetting what he did. There's nothing wrong with showing what you think and believe in.