So I caught a few videos by a couples counselor on YouTube who specializes in infidelity and he made a short one about 3 questions your WS should be able to answer, or at least be working on answering if reconciliation is possible.
1. What broke in you?
What is broken inside of you that made you feel like having an affair was a good idea? Not talking about what was going on in your marriage, or the state of the relationship. Those are just excuses. What is going on inside of you that allowed you to drop your boundaries and go against your own moral code? Some answers could be "I have always avoided difficult conversations, so instead of telling you that I was unhappy in our relationship, I escaped into someone else's," or "I've never dealt with my need for external validation, so when someone else showed me attention I couldn't resist," or "I grew up in a house where lying was how we survived so I never really learned how to be honest."
2. What are you doing to fix it?
How can I know this won't happen again? What steps are you taking to fix whatever is broken inside of you to ensure you're addressing your issues? Are you examining your boundaries? Are you in counseling? Are you actively fixing what you broke and making sure it will never happen again? Some answers could be "I'm in IC working on my conflict avoidance," or "I'm reading about attachment patterns," or "I'm learning how to communicate discomfort instead of escaping it," or "I'm being completely transparent with you. You have access to everything."
3. What do I need that you're not giving me?
A truly remorseful spouse is watching you and studying you. They're paying attention to your triggers and figuring out what upsets you. They're trying to get inside you and figure out what it is you need to feel safe again. Are they blaming you for their choices? Are they reducing triggers? Some answers could be "you need more reassurance from me," or "you need me to stop being defensive when you ask questions," or "you need me to take ownership without bringing up problems in our relationship."
If your WS can't or won't answer these questions thoughtfully without blaming you or the relationship then you don't have much to work with. They should be learning your landscape of pain so that they know what's causing it, and be taking proactive steps to fix what they've broken instead of avoiding it.
If they can't answer these questions, or at least be working on how to answer them then you may be in for a really rough ride.
This is all according to Wes White, and he really does touch on alot of what we discuss here. His YT channel is "Wes White Counseling" and he has several videos on infidelity ranging from 5 to 15 minutes in length.