You were not stupid, do not blame yourself for triggering. I am where you are, I have a similar DDay, feh had a LTA that lasted for almost five years and A ended on DDay. I have had four days in a row in which I have triggered badly. Today was a better day.
We are still figuring out the new normal. I feel like when things are improving I have the urge to remind myself of how badly fwh hurt me so that I can protect myself. It is completely understandable to want to save your self from further harm.
I used to keep the messages from my fwh online. But I have since saved them to a flash drive and printed off hard copies and locked them into a box in a garage and placed them in a high location where I need a ladder to access them. I have also placed copies into my safe deposit box in a bank. I then deleted the copies from my hard drive. I did this not to hide this from fwh, he knows I have copies and will use them if needed. I will never forget what is contained in those texts and emails. I did this because in a flash of anger it was too easy to throw them into fwh face. Don't get me wrong, fwh is remorseful, regretful and is doing everything he can to rebuild trust and ultimately our M. He acknowledges the contents of the texts and has never denied doing it. There was nothing to be gained by throwing the texts in his face.
Was there a particular reason why you looked through the messages today? If you WH is doing all of the things you need, and no red flags are going off maybe consider moving the phone to a less accessible location. I am not advocating getting rid of the phone, you never know when you might need it. But for me, by moving the phone to a less accessible location forces me to really consider whether I truly need to read the messages again and bring back all of the pain.
Finally, try and forgive yourself for trusting and believing in someone you loved. The fault lies with him, not you. I am working on this too, in hindsight, I cannot believe some the lies I accepted. It seems ludicrous now. It is not wrong of you to share your anger and pain with him, he needs to own this.
I hope I am making sense. You are not alone and I will be following this thread for advice. Thank you for sharing.