First, I am extremely avoidant of emotionally uncomfortable situations. My upbringing was such that the avoidance is ingrained.
This I can relate to... my avoidance of discomfort manifested in an addiction, even. Perhaps you need to ask your BS to hep you make a safe place to share your feelings. Your avoidance is likely rooted in fear, so creating a safe place is important. This could be done by going to couples' counseling, or this could be done by setting conversational boundaries-- things like being able to call a timeout, or "whoever is holding the pillow gets to speak uninterrupted until they pass the pillow," Imago dialogue, etc.
I also find it incredibly exhausting to hold discussions without getting defensive, etc.
If you're like me, this will help: Ask you BS for some affirming words before lacing in with the criticisms. Are you familiar with the five love languages concept? My guess is that your love language is "Words of Affirmation" and that critical words actually dig deeper to you than they do to her. This doesn't mean she has to avoid all criticisms, but it means that you need some positive affirmations sprinkled in-between the negatives so that you don't shut down and kick in to super defensive mode. ...Also, read that book. It's good.
I don't feel confident that I've given you helpful information. So maybe more important than anything, I get to tell you that I feel your pain. I've been there, man. It's really really hard-- it's gut-wrenching-- it's exhausting.
One last thing-- I do think the chance for reconciliation is a great gift you're receiving. Try to see how brave it is of your BS to come to you scared, hurt and angry... and then to show you such great love by attempting to reconcile. Just her presence is brave of her. Talk about wanting to run away from uncomfortable emotions!... she's resilient. Make sure you remind yourself of that before you engage in conversation. Try to match her resilience and courage.31yo WS-SA
ďWhen we disclose the thought and intents of our hearts in surrender, we identify with one another at depth.Ē