I didn't read all the responses right through but I wanted to answer your original question.
When my H first tried to explain to me that he lacks empathy it sounded like an easy fix to me: pay attention. Pay some fucking attention to what other people are saying and then just literally imagine how you would feel if you were them.
For anyone who DOESN'T struggle with empathy like, of course, right?
I think the two situations you are describing are both problematic because what neither spouse is doing is working through the problem.
I want to put up walls, yes. But it doesn't help in the long run, so even when my husband was not a safe partner and I KNEW he wasn't, I still shared my feelings with him as clearly as I could. Sometimes this manifested as yelling or sobbing but as much as possible I worked on speaking his language: Here is the situation. I want this. I did this and this to try to get it. You responded in this way and that made me feel this.
If I lose my composure, he just mentally hides from it.
If I don't share, yes, I'm wallowing. This is like being stuck in a loop. You get to the most intense part of this feeling and instead of doing something about it, you just start the feeling over again and again and make yourself sick. Wallowing or marinating in this feeling is just making it easier to find the next time I go back. Talking it out helps me to move on from what I can.
That brings me to the next thing I do which my husband and his IC both think is insane: Recreating situations, visiting places, going over details from the past. When I start wallowing and don't feel like I'm making progress, I go over my information. What are the things that are still bothering me? How can I break them down into smaller pieces and put some of them aside? I could never forgive and forget the whole affair at once. But recently there was an event we missed because the affair was ongoing when we were supposed to RSVP. Leading up to the event I was angry that it was one more thing I couldn't do because of the affair. Once it was over and past, I started to feel like it didn't matter anymore. So I went to my husband and explained "I was mad about this. But I'm ready to forgive you for this." He didn't know I was mad before I forgave him. But it helped me to put the final lid on it. If I don't ask myself how something makes me feel and define that as narrowly as possible, it just lingers and sours everything.
The opposite end of this spectrum is the "just don't think about it" and I fully agree with you that this is just a way to get back into trouble. I think our WSs did enough "not thinking about it" when they were out cheating on us and ignoring how much their behaviour would hurt others. But the answer isn't wallowing. It's just considering.
I have never done this but I read about this exercise where the two people calmly sit together and the one talks about their feelings, and the other person can't argue, explain or deflect, but just listen. Look at the person talking and the only response is "Thank you for telling me", no matter what the other person says. Once it's all completely done they take a break to be quiet and then it's the other person's turn. I don't know if it helps but it certainly can't hurt. She needs to think about her actions and how to avoid repeating them. She needs to think about your feelings and how to support you. Lots of the books and strategies everyone brought up will help with this.
I hope your communication improves. I really want to believe that ours will. Some days that is exquisitely overwhelming, to have someone I have loved for half my life telling me that he has no feelings. Apparently I was just here all by myself, living out my life talking to myself, and he was all along just wondering if there was anything good on TV.