IB all I ever seem to post to you is that I know how it feels! Except no-one else really does.
The sense of nothing else to give, the double whammy of divorce and empty nest, the sense of personal failure and hopelessness. I still sometimes get these, but now I know they will pass. And as your children get older [I had a very very rocky time with my second and third sons who felt utterly let down in every sense by their walk away father] they will tell you how much they admire and respect you. They come to see that being the responsible parent is hard.
My xh was a real walk away dad. now he is much more interested in being in their lives, but has left it a bit late. They allow him in, but he is definitely second division. Oddly enough I find this hard too.
So yes, I can empathise with what you are feeling, and suggest that you really spend some quality 'me' time, having loked after everyone else. what you invest in yourself pays back dividends. hard to believe before hand that a wonderful haircut and classy new shoes will make such a difference!!
