I sent her a validation letter, while pointing out her behavior hurt me. She wrote back that she sees how her actions really hurt me. She explained that while it's not much better, she planned to break up with me before she met him. She kept it an EA while we were still living together despite his advances (from what I saw it all checks out).
I still want to try to get her back (if she does it again, then shame on me). So what's my next step? Do I email her back and keep validating (I totally see how I neglected her feelings for 1.5 years)? Do I tell the OM's spouse to get him out of the picture?