DO. NOT. PANIC. (Any more than you already have.) Don't file yet. This affair is likely to fail, but it takes time. Hold on to the M for now, but like the rest of us you'll have to start moving on with your life. You do need a lawyer, but DO NOT MAKE ANY HASTY DECISIONS. You will feel different tomorrow and different again on Monday. Not necessarily better, unfortunately, but you will have glimpses of better times soon.
I am so, so sorry. It's got to hurt like he!!.
Also, go dark and don't respond to him. Let him sit with this. He doesn't need to know anything now.
DO NOT RESPOND TO HIM.
11/4/15 W revealed EA/2 months later became PA with co-worker Reconciling since late April 2016 Don't give up until it's time, then move on Be patient, strong and kind but never a doormat