If there are no children and no property involved, you likely don't need a separation agreement unless one of you is entitled to spousal support. My STBXH and I did one and it will just be applied to the divorce in May with no extra paperwork needed since we already dealt with property and custody/access to our children. Sorry things are going down this way. I remember how much it hurt when everything was at its peak in my sitch. I am happy to report, however, there is life after separation/divorce. I barely think of my STBXH at all these days. NEVER did I think I would get here but I did and my life is much much better without him than it was with him. His GF is welcome to him.