It's wonderful that you have gotten an apology from XW. At the very least it is a peek out of the tunnel.
I agree with Cadet that your XW has dipped her toe in to temperature check.
I don't think you need to give much thought about whether you'd reconcile or not at this point. I read nothing in the message that she sent you that she was thinking along those lines.
Personally, I would be thrilled if my H sent a message like that because I would take it like he at least had started to come out of himself enough to start to survey the destruction his choices had caused.
I agree with the others that a short note accepting her apology, forgiving her, if you truly can, and thanking her for it would be the way to handle this at this time. It is the groundwork that is laid for whatever future R you decide to have with XW.
From there, you will be able to view her actions without really investing your heart again. As this unfolds further you'll be able to judge whether or not she is truly waking up and willing to do the work it would take for you to even consider reconciling. You have a lot of time to come to a decision, MHL.
I truly hope this is the beginning of the bridge that helps your D and XW start to rebuild a relationship with.
As far as guarantees that something like this would never happen again IF you were to R with your X, well you don't get one, none of us do with any R...
You're a good man MHL, and I wish you all the best.
