No legal proceedings needed to separate, it is really simple practically. But of course emotionally it is (for me at least) not much easier after such a long time (we moved in together after dating for 3 months and have been living together ever since besides the other 2 times she had to take a break).
Remember, you cannot make someone love you. The sooner you come to grips that maybe she does only love you like a brother, the sooner the emotional side of this will begin to subside.
Hang in there 1st, you are going to be fine no matter what.
What Steve wrote here is all you need right now. No marriage, no kids. Take this BD as a wake up call. You didnt change the last two times. If you dont change there never was and never will be a chance. Do this for you and down the road she might come back or you'll have improved for a better life with someone else.
What you described above is not a 180 IMO. 180 isn't about behavior from the past few weeks. It is about changing real habbits and ways of acting that have characterized you since you moved in together. Changing YOU. At this point interaction should be ZERO anyway.
Me: 34 Stbxw: 30 D:5 D:3 Mini bd: May/June 2019 Married: Aug 2019 BD: 6th Dec 2019 OM Confirmed: Feb 2020 March 2020: I filed for D Waiting for D to be finalized and W to move out end of January 2021