Like you I thought and still think that my xh was the love of my life. We have known each other a very very long time, and were married a very long time . . . . Even if I got together with someone else we would not have the history, shared memories and the children.
Not saying we can't have new relationships, but time is a dimension that we just cannot ignore.
Again like you my xh has no interest in me. I could fall off a cliff tomorrow and it would barely register. I had major surger a couple of years ago and he didn't take any interest at all. The old xh would have been camped out at the hospital. Where does it all go? I know there is no answer and we can only go on with our lives, but it is frightening that what you thought was rock solid looks like an illusion.
Fwiw I do not think it was an illusion, I think we were loved, and something is very wrong with their current emotional state. but it is their life, and we cannot help them or fix them. But I do not stop loving the man I was married to. It is the alien in his body i struggle with even liking!