I'm so sorry, OP. I've been through it, too. Yes, just another dissatisfied, middle-aged malcontent, thinking he's too good for his wife all of a sudden.
I disagree with those saying it's all fine and dandy to leave the relationship if you're not happy. What is the sodding point of the sodding marriage vows, then? Absent abuse or neglect, you're supposed to work at it.
You have every right to feel aggrieved, OP. Yes, you will be OK, and better off without someone who has shown such a lack of commitment and care towards you, but I think those who have not been divorced, especially after a long marriage, cannot appreciate how totally it bifurcates your life. Your entire future that you thought you could rely on as a guiding beacon through the present is gone. Where's the lighthouse? It's gone dark, and you have no idea where the rocks are. Where there was a future, there's just empty space. Nobody who hasn't been through it can understand the scale of the adjustment required.
Unless you have cheated on your spouse or abused him in some way, including longterm neglect, then I think ending a marriage is a moral crime, I really do.
I dearly hope he comes to regret this.