Sweetie, come on and sit next to me on the sofa. The Big Sofa where we process stuff together.
It seems that you are reeling from XH's latest revelations and self-realizations. Right now, it is imperative not to make any assumptions about his motivations or intentions. Unless you've lived inside his head, you really just DON'T know at all.
Frankly, I do not see it as XH making any resolutions or taking firm steps toward one particular outcome. At that time, I believe he was sincere in expressing his remorse which is a BIGGIE for an MLCer. Now, I am with you on setting boundaries and keeping them for now as a self-protective measure. I get that. Good job on keeping XH outside in the front door and not letting him inside. He's going have to do some more internal and external work to earn your trust again after all of that awful stuff he's pulled out over the last several months/years.
However, I wouldn't be too hasty in slamming the door in his face because he didn't meet your expectations of doing E,F, G in that precise order or in a particular way. Take his words at the face value for now.
What you really do need right now is to step back to process your emotions. Your emotions are trying to tell you something and you react by wanting to write a letter to XH because they are very uncomfortable with you.
What I do when faced with uncomfortable emotions is to sit on the Wounded Child Sofa and have a chat with her about what's going on. I'd bet the Kent Farm that you'd find a bunch of stuff that you didn't know were there all along.
Own your emotions. Own your reactions.
Step back for a bit. There is no firm timeline or deadlines for time is an illusion. There is NO urgency here, Pink.
It helped me to realize that my marriage is totally over, and it is not going to be the next "Walking Dead" episode. It is gone, won't ever be back.
This ^^^ is your Wounded Child crying out loud. It doesn't necessarily mean it's totally over. Not from where I am sitting. It is a new trajectory. That new line is not yet being written. At this time, it is a new energy for you and XH. How you two handle it is UP to you.
I can understand your fear: being really hurt ALL over again if you were to open up your heart again to XH. I had the very same reaction when Ms. Wonka and I communicated again. I went a bit stir crazy and Fort Knoxed my heart with a bunch of spikes in the road and other gazillions of booby traps to prevent Ms. Wonka from entering my heart again.
If he wants to give a second time chance to "US" as a couple, a family... then he knows my address.
Honey, it goes both ways. You also need to be at a place to given XH a second chance as well. It takes two to tango for a reconciliation.
However, it is critical that you go into self-care and allow time to process these emotions. No decisions need to be made today. Next week. Next month. Allow it all to unfold organically.
Instead of a letter to XH, you might want to journal to yourself to better understand the latest revelations and what they mean to you. Whatever works for you.