Op there are many ways in which men who still want to appear the victim or keep their options open will engineer their time or space away from the home.
Many men provoke women till the situation at home is untenable, none of this is your fault, no nagging nothing would have stopped this steam train of selfishness that he is on.
It's hearbreaking, if they leave or even if they return.
If they do come back having a period of enlightenment, it may feel like relief for a short while but it's like a Band Aid, it just covers up the scar but it 's still there and the pain remains.
I understand you are poleaxed in your grief, but this is what he is banking on.......
YOUR FEAR
Your fear keeps the status quo for him and believe me if he came back with no consequences he would be the most self entilted arogant bastard ever!
He is banking on your fear.
Fear that you will not finalise anything in writing by seeing a solicitor.
He needs the threat.
Even if you set the ball rolling for divorce, you can stop the process if you wish if things change.
I personally think he's an obnoxious man, and you sound loyal , dependable and are a credit to your family.
Youv've got this op your better than him.