SC, my friend, I know you are in pain, of course you are. This is hard stuff. Really it is. Your h is in MLC. That is obvious. So, DBing still applies. This is for you, not him.
Dont keep analyzing and trying to figure out why h is where he is. It doesnt really matter. What matters is you and your family. That is why it is so important to detach, GAl and try to keep a positive attitude - for you.
I personally dont think you should be dating. You are not emotionally in a good place right now. There is no hurry. Do it when it feels right to you, not because MIL or anyone else says it is.
Sweetie, take it one day at a time. Get through each day, focusing on you.
Your marriage and memories are real. He is in crisis right now and needs to take his own journey. And you need to take yours.
S, please dont call him, dont keep giving him so much head space. And you never have to explain or justify to us why you are feeling like you do. This is a crazy ride, full of ups and downs and remember we all backslide and we are here for you.