Also... Being a "nice" guy in the sense that you mean it -- that's a matter of tiny decisions made in the moment as you go through your life. A woman who wants to be her best self in a relationship isn't going to accept "nice" behavior -- because your happiness will be a priority for her. So asking why your W would want to get back together with a nice guy isn't really a productive question. The Stockdale paradox and acknowledging that "I'm already dead" will make it easier for you to make the changes that make you stronger and reduce the fear that you can do anything to make things worse than they already are.
Whether those changes will win your W back is an open question, but she sure doesn't seem like someone who wants to be her best self.
Take your power back, Not So Old Dog. Be the man you want to be by taking the time you need to choose to in any given moment.
And FWiW I agree with Raliced.
Me42, H40 D12, S8, S7 A revealed: 7/13 Sep 4/14; Agreed to D 1/15