I think you are mixing up the intellectual with the emotional element. I have no fear of abandonment at the intellectual level. I have lived single, I can live single again, though I prefer not to. Live will go on and I could possibly be even happier than I am now. There will be consequences concerning the kids that I may not like, only seeing them part time, every other year not having them for Christmas, etc. I know that once in that situation, I can just adapt.
But that is not the issue. I still FEEL anxiety when I think of this or other related issues. It is the conditioned reaction I have from years of growing up in a dysfunctional family. Do you have anxiety over the thought of getting a shot? There is a little pain, but really it is not so bad (unless it’s a gamma globulin shot or something huge like that). For some people, the thought of getting a shot is much worse than the reality. It is a conditioned response, usually from a past experience. It can be overcome, but it takes some training.
Reacting to our marriage issues is the same thing. I believe it is rooted in fear of some sort. That fear does not need to be valid, especially as an adult. But the reaction is automatic and continually pushing that hot button does not help.