W just left. Told me that over the years as we fought, she lost her respect for me and that it hurt a little less every time. We only fought a couple times a year, over the same stuff every time. So I would guess that I need to regain her respect first. We can still talk like best friends, should I 180 there and close myself off?
The more you act like a best friend, the less chance you have of turning this around. You're letting her have the good parts of you without having to commit anything. You're showing her that she still has you wrapped around her finger and can get what she wants from you.
So you can be friends if you want. But I don't think that will save your M.