U, Fade is not being alarmist at all. He is offering good, sound advice based on having seen many similar situations play out over the years. As you'll recall many of us suggested not moving out in the first place, but I completely agree with him that if you do move out, you should put an agreement in place because once you move out you have zero negotiating leverage and will have to live with whatever scraps your W decides to throw your way.
I am not sure why you see a written separation agreement as divorce. That's not it at all. It is simply an agreement working out the details of the separation. It's common practice. I did one with my XW when she moved out. We didn't get D'd until nearly 2 years later. You need to quit looking at everything emotionally and detach and look at it like a business transaction because that's really what it is.