I have been in the middle of a divorce since Aug. To be honest I wish I had done the separation agreement. But my situation is very complicated so one could not be done. So If both you and him are in agreeance of the separation and you have children a home, bills, cars, etc..yes I would say get one. Because the agreement will be that first step in getting those issues resolved. (who pays what, child issues, money issues etc.) If you do not have any of the above issues you can just go directly to filing for a divorce. As far as leaving the state. I was told there was no problem with it as long as I didn't have children involved. Again this issue is solved with the separation agreement and other paperwork that your lawyer can look into. Your husband though can say no, fight it and you will have to stay in the state until the divorce is final. Hope that helps some.
As far as the abandonment issue I have learned this. My husband walked out on me. His lawyer knew it my lawyer knew it. I have placed that as reasoning for my divorce. BUT the main reason why is because he left without keeping up with the household obligations. If he had left and kept up with the mortgage, and other bills he wouldn't be found guilty of it if brought up in court. Bottom line is this, if you leave don't leave him stranded to pay for everything help out with the obligations until you and him have hashed out on a legal document (the separation paper) who is doing what. :-)