Viewing this person as severely losing touch with reality would help me detach.
weve all been there. it would almost certainly ease the pain; im not sure its a balanced approach to detachment, especially if its not the entire reality itself.
you know the Ten Forms of Twisted Thinking very well. this is a form of painting our exes black - in this case, "black"=broken, hopeless, crazy, disturbed, or severely losing touch with reality. i did it myself. the hook in this line of thinking is that it puts us in a one up, superior position (a leftover relationship dynamic in many of our cases, certainly mine).
i get it. its a tempting line of thinking: if our exes are hopelessly broken, or evil, or psychotic, or whatever adjective, then how could we possibly feel for them? yet we do. at the end of the day it doesnt pass the reality test, it doesnt line up with how we saw or see them. to convince ourselves otherwise is building a shaky foundation for our healing.
grieve the person, grieve the loss, feel the feelings; face the facts. it will hurt, there is pain involved in getting to that elusive stage of freedom. and we are here for every step of the process.